Williams Hematology


Arsenic Hydride
Miscellaneous Drugs and Chemicals
Insect, Spider, and Snake Venoms
Chapter References

Arsenic, lead, copper, chlorates, and a variety of other chemicals can cause severe red cell destruction, and hemolytic anemia is a part of the clinical syndrome associated with intoxication by these substances. Arsenic may cause hemolysis by interacting with sulfhydryl groups. Lead inhibits a variety of red cell enzymes, including several enzymes of porphyrin metabolism and pyrimidine-5′-nucleotidase. The anemia that it produces is usually not primarily hemolytic in nature. Copper inhibits a number of red cell enzymes and catalyses the oxidation of intracellular GSH. Chlorates produce methemoglobin and Heinz bodies. There are many drugs that have appeared to cause hemolytic anemia, usually by unknown or poorly defined mechanisms. Animal toxins, such as those elaborated by insects, spiders, and snakes, may also cause hemolytic anemia. Hemolytic anemia is a common accompaniment of severe burns, probably as a result of direct damage to erythrocytes by heat.

Acronyms and abbreviations that appear in this chapter include: ALA, aminolevulinic acid; EDTA, ethylenediaminetetraacetic acid; GR, glutathione reductase; GSH, reduced glutathione; G-6-PD, glucose-6-phosphate dehydrogenase; NADPH, reduced nicotinamide-adenine dinucleotide phosphate.

Many drugs and a variety of toxins have been associated with red cell destruction. Hemolysis that results when certain drugs are administered to patients deficient in glucose-6-phosphate dehydrogenase or with unstable hemoglobins is discussed in Chap. 45 and Chap. 48. Immune mechanisms may also play a role in drug- or toxin-induced hemolytic anemias. Such hemolytic anemias are discussed in Chap. 57. Microangiopathic hemolytic anemias (Chap. 51) may also be caused by drugs such as mitomycin.
The present chapter deals with drugs, toxins, and other physical agents that can cause red cell destruction by other mechanisms, or by mechanisms that are not understood at present.
The inhalation of arsine gas (arsenic hydride, AsH3) is a well-recognized cause of hemolytic anemia.1,2 Arsine is formed during many industrial processes. Most commonly it results from the reaction of nascent hydrogen, generated by the action of acid on metal, with arsenic compounds. The arsenic is usually present as a contaminant of either the acid or the metal, so that the contact with arsenic compounds may not be apparent from the history. Exposure to sufficient amounts of the gas will lead to severe anemia, jaundice, and hemoglobinuria. The mechanism of hemolysis is not clearly understood, although the well-known reactions of arsenic compounds with sulfhydryl groups in the cell membrane may play an important role.
Lead poisoning (plumbism) has been recognized since antiquity. The ingestion of beverages containing lead leached from highly soluble lead glazes or earthenware containers has been blamed for the decline and fall of the Roman aristocracy and is even now an occasional cause of lead intoxication.3 The distillation of alcohol in leaded flasks is another rare cause of plumbism in certain areas, although the practice was prohibited in 1723 by the Massachusetts Bay Colony after it was noticed that consumption of rum so distilled resulted in abdominal pain known as the “dry gripes.”3 Among the earliest published descriptions of lead poisoning is a letter written in 1786 by Benjamin Franklin4,5 who had learned as a printer that working over small furnaces of melted metal or drying racks of wet type in front of a fire might cause pain in the hands. Today, lead intoxication in children generally results from ingestion of flaking lead paint or from chewing lead-painted articles. In adults, it occurs primarily as the result of inhalation of lead compounds used or produced in industrial processes6 as in battery manufacture,7 but poisoning may occur as a result of leaching from pottery or dishes that come in contact with food.8,9 Restoring tapestries and producing pottery and tiles10,11 have also caused lead poisoning. Most patients with lead poisoning manifest some degree of anemia, although anemia is only rarely the predominant clinical manifestation.12 However, examination of the blood often provides the key diagnostic clue, and thus the hematologic findings are of special interest. Modest shortening of red cell life-span is a relatively constant feature of the disorder.13,14 In vitro treatment of red cells with lead produces measurable membrane damage: lead interferes with the cation pump,15,16 possibly in inhibiting membrane ATPase.17,18 It is not at all clear, however, that the hemolysis observed in lead poisoning is due to these changes. In some children with lead poisoning, an electrophoretically fast moving hemoglobin indistinguishable from hemoglobin A3 comprises approximately 15 percent of the total pigment.19
The anemia of lead intoxication is not usually due primarily to hemolysis. Lead apparently interferes with the normal production of erythrocytes, probably through a combination of mechanisms. Heme synthesis is markedly abnormal in patients with lead poisoning. Several enzymes of heme synthesis are inhibited, including d-aminolevulinic acid (ALA) synthetase, ALA dehydrase, heme synthetase, porphyrinogen deaminase, uroporphyrinogen decarboxylase, and coproporphyrinogen oxidase.12,13 ALA dehydrase has been considered particularly sensitive to inhibition, showing decreased activity in erythrocytes at blood lead levels in the upper portions of the normal range,17 but its sensitivity at low blood lead levels has been questioned.20 Increased amounts of d-aminolevulinic acid and coproporphyrin are found in the urine,21 and the free protoporphyrin levels22 of the erythrocytes are strikingly increased, presumably as a result of inhibition of the heme biosynthetic enzymes. Marked inhibition of the enzyme pyrimidine 5′-nucleotidase is also observed.23,24 In the absence of this enzyme, pyrimidine nucleotides accumulate in the red cells and normal depolymerization of reticulocyte ribosomal RNA does not occur. In hereditary pyrimidine 5′-nucleotidase deficiency, basophilic stippling of erythrocytes is a characteristic finding (Chap. 45), and it has been suggested that inhibition of pyrimidine-5′-nucleotidase by lead may be responsible for the basophilic stippling of erythrocytes that occurs in plumbism (see below). Inhibition of activity of the hexose monophosphate shunt has been documented.25 Synthesis of a- and b-globin chains seems to be defective in lead poisoning,26 and this may play a contributory role in the anemia of lead poisoning.
Remarkably complete observations of the acute hematologic changes occurring after the intravenous injection of lead in an attempt to treat malignant disease were published in 1928.27 Distortion of red cells was observed both in blood films and in wet preparations made immediately after infusion of lead. This was characterized by a “folding” that made the cells appear as semicircles, clumping, and the presence of “bite cells.” The anemia of chronic lead poisoning is usually mild in the adult but is frequently more severe in children. A relatively close relationship exists between blood lead levels and the hematocrit.28 The red cells are normocytic and slightly hypochromic. The hypochromia may be due to coexisting iron deficiency.29 Basophilic stippling of the erythrocytes may be fine or coarse, and the number of granules seen in each cell may be quite variable. When blood is collected in ethylenediaminetetraacetic acid (EDTA; “purple top” tube), as is commonly done, the stippling may disappear.30 Young polychromatophilic cells are most likely to be stippled. Electron microscopic studies31 have demonstrated that the basophilic granules represent abnormally aggregated ribosomes. In the marrow, ringed sideroblasts (Chap. 22) are frequently found. Iron-laden mitochondria are present31 but do not appear to contribute to the basophilic stippling that is observed on light microscopy. It may be presumed that iron entering the developing erythroblast fails to be incorporated into heme at a normal rate, either because of lead-induced impairment of heme synthesis or because of the direct effect of lead on mitochondria.
Meso 2,3-dimercaptosuccinic acid, an orally administered chelating agent has been used to treat lead poisoning.32,33
Hemolysis has also resulted from ingestion of copper sulfate in suicide attempts and from accumulation of toxic amounts from hemodialysis fluid contaminated by copper pipes.34,35 Hemolysis in Wilson disease has been attributed to the elevated plasma copper levels characteristic of that disorder,36,37 and 38 and hemolytic anemia may be the presenting symptom.39,40 The pathogenesis of this hemolytic anemia may be related to oxidation of intracellular GSH, hemoglobin, and NADPH and inhibition of glucose-6-phosphate dehydrogenase (G-6-PD) by copper.41 However, the amount of copper required to inhibit G-6-PD is large, and copper in much lower concentrations inhibits pyruvate kinase,42 hexokinase, phosphogluconate dehydrogenase, phosphofructokinase, and phosphoglycerate kinase.43 Plasma exchange has been used successfully to treat the hemolytic anemia of Wilson disease.44
Sodium and potassium chlorate are oxidative drugs which have been known to produce methemoglobinemia, Heinz bodies, and hemolytic anemia. While it might be presumed that the mechanism of hemolysis is similar to that resulting from other oxidative drugs, no cases have been observed in patients deficient in G-6-PD. The rare instances of chlorate poisoning that have been reported usually resulted from prescription errors in which sodium chlorate was dispensed instead of sodium chloride.45 Hemolytic anemia with Heinz body formation has also occurred in patients undergoing dialysis when the tap water used contained a substantial amount of chloramines. Oxidative damage of the red cells of these patients was demonstrated by the presence of Heinz bodies, a positive ascorbate-cyanide test, and methemoglobinemia.46,47 Leaching of formaldehyde from plastic used in a water filter employed for hemodialysis is also a cause of hemolytic anemia. It was suggested that the effect of the low levels of formaldehyde found in the water were not mediated through its fixative effect but rather by inducing metabolic changes in the red cells.48
There are also isolated reports of hemolytic anemia occurring after the administration of a variety of other substances, listed in Table 53-1.


Hemolytic anemia produced by phenazopyridine is often associated with “bite cells” and “blister cells.”67 When large amounts of distilled water gain access to the systemic circulation, either by intravenous injection or when used as an irrigating solution during surgery, hemolysis will occur.68 Severe hemolysis may also result from water inhalation in near-drowning.69
Hemolytic anemia has been observed in astronauts exposed to 100 percent oxygen; a reduction of red cell volume also occurs when the O2 tension is maintained at normal atmospheric levels, and this is believed to be due in some unknown way to weightlessness.70 In at least one patient, hyperbaric oxygenation was associated with acute hemolysis.71 It was suggested that hemolysis in this instance may have been due to abnormal peroxidation of lipids in the erythrocytes, but evidence supporting this view was indirect and equivocal.
Bee72 and wasp73,74 and 75 stings have been associated with severe hemolysis, and spider or scorpion bites have occasionally been followed by hemolytic anemia and hemoglobinuria.76,77,78,79,80 and 81 The spiders usually thought to be responsible are Loxosceles loeta and Loxosceles reclusus. It is unknown why some patients suffer hemolysis after insect bites whereas others do not. Although snake venom may cause hemolysis in vitro by converting lecithin to lysolecithin (see Chap. 27), hemolysis does not often result from snake bites,82 and when it does occur, it may represent microangiopathic hemolytic anemia associated with coagulation abnormalities induced by the venom.83
It has been known for over a hundred years that heating blood to temperatures above 47°C (117°F) rapidly produces visible damage to erythrocytes. The sequence of events has been defined in detail.84 Cells damaged by heating not only show morphologic changes and increases in osmotic and mechanical fragility but are also removed rapidly after reinjection into the circulation.85 These observations explain the severe hemolytic anemia which occurs in patients with extensive burns. Spherocytosis and increased osmotic fragility are found in many patients, and blood films may show fragmentation, budding, spherocytosis, and severe microspherocytosis. These changes are particularly evident if films are made promptly after the burn occurs. Gross hemoglobinemia was observed in 11 of 40 patients with second- and third-degree burns involving 15 to 65 percent of the body surface.86 It seems likely that the acute hemolytic anemia occurring within the 24 h following a burn is due to the direct effect of heat on circulating erythrocytes. Hemolysis occurring more than 24 h after the burn may sometimes be due to the infusion of isoagglutinins (particularly anti-A) in pooled plasma, when this has been administered to the patient as part of treatment,87 or be the result of infection or coagulation disorders that are common complications of extensive burn injury.
Although reduced red cell survival is a part of the complex series of events occurring after administration of large doses of total body radiation,88 erythrocytes appear to be very resistant to the direct effects of radiation.89 Such shortened red cell survival as may occur after radiation is probably related largely to red cell loss through internal bleeding and to various secondary events such as infection.

Phoon WH, Chan MO, Goh CH, et al: Five cases of arsine poisoning. Ann Acad Med Singapore 13(2, suppl):394, 1984.

Romeo L, Apostoli P, Kovacic M, Martini S, Brugnone F: Acute arsine intoxication as a consequence of metal burnishing operations. Am J Ind Med 32:211, 1997.

Klein M, Namer R, Harpur E, Corbin R: Earthenware containers as a source of fatal lead poisoning. N Engl J Med 283:669, 1970.

The Complete Works of Benjamin Franklin, edited by J Bigelow, Putnam, New York, 1888.

Andreasen NJC: Benjamin Franklin: Physicus et medicus. JAMA 236:57, 1976.

Staudinger KC, Roth VS: Occupational lead poisoning. Am Fam Physician 57:719, 1998.

Froom P, Kristal-Boneh E, Benbassat J, Ashkanazi R, Ribak J: Predictive value of determinations of zinc protoporphyrin for increased blood lead concentrations. Clin Chem 44:1283, 1998.

Autenrieth T, Schmidt T, Habscheid W: Lead poisoning caused by a Greek ceramic cup. Dtsch Med Wochenschr 123:353, 1998.

Kakosy T, Hudak A, Naray M: Lead intoxication epidemic caused by ingestion of contaminated ground paprika. J Toxicol Clin Toxicol 34:507, 1996.

Fischbein A, Wallace J, Sassa S, et al: Lead poisoning from art restoration and pottery work: unusual exposure source and household risk. J Environ Pathol Toxicol Oncol 11:7, 1992.

Vahter M, Counter SA, Laurell G, et al: Extensive lead exposure in children living in an area with production of lead-glazed tiles in the Ecuadorian Andes. Int Arch Occup Environ Health 70:282, 1997.

Harris JW, Kellermeyer RW: Acquired abnormality: Porphyrinuria, in The Red Cell, p 35. Harvard University Press, Cambridge, 1970.

Waldron HA: The anaemia of lead poisoning: A review. Br J Ind Med 23:83, 1966.

Westerman MP, Pfitzer E, Ellis LD, Jensen WN: Concentrations of lead in bone in plumbism. N Engl J Med 273:1246, 1965.

Khalil-Manesh F, Tartaglia-Erler J, Gonick HC: Experimental model of lead nephropathy. IV. Correlation between renal functional changes and hematological indices of lead toxicity. J Trace Elem Electrolytes Health Dis 8:13, 1994.

Vincent PC, Blackburn CRB: The effects of heavy metal ions on the human erythrocyte. I. Comparisons of the action of several heavy metals. Aust J Exp Biol Med Sci 36:471, 1958.

Hernberg S, Nikkanen J: Enzyme inhibition by lead under normal urban conditions. Lancet 1:63, 1970.

Hasan J, Vihko V, Hernberg S: Deficient red cell membrane Na+ + K+-ATPase in lead poisoning. Arch Environ Health 14:313, 1967.

Charache S, Weatherall DJ: Fast hemoglobin in lead poisoning. Blood 28:377, 1966.

Chalevelakis G, Bouronikou H, Yalouris AG, et al: delta-Aminolaevulinic acid dehydratase as an index of lead toxicity. Time for a reappraisal? Eur J Clin Invest 25:53, 1995.

Goldberg A: Annotation. Lead poisoning and haem biosynthesis. Br J Haematol 23:521, 1972.

McElvaine MD, Orbach HG, Binder S, et al: Evaluation of the erythrocyte protoporphyrin test as a screen for elevated blood lead levels. J Pediatr 119:548, 1991.

Paglia DE, Valentine WN, Dahlgren JG: Effects of low-level lead exposure on pyrimidine 5′-nucleotidase and other erythrocyte enzymes. J Clin Invest 56:1164, 1975.

Aly MH, Kim HC, Renner SW, et al: Hemolytic anemia associated with lead poisoning from shotgun pellets and the response to Succimer treatment. Am J Hematol 44:280, 1993.

Lachant N, Tomoda A, Tanaka KR: Inhibition of the pentose phosphate shunt by lead: A potential mechanism for hemolysis in lead poisoning. Blood 63:518, 1984.

White JM, Harvey DR: Defective synthesis of alpha and beta globin chains in lead poisoning. Nature 236:71, 1972.

Brookfield RW: Blood changes occurring during the course of treatment of malignant disease by lead, with special reference to punctate basophilia and the platelets. J Pathol 31:277, 1928.

Schwartz J, Landrigan PJ, Baker EL, Jr., Orenstein WA, von Lindern IH: Lead-induced anemia: dose-response relationships and evidence for a threshold. Am J Public Health 80:165, 1990.

Clark M, Royal J, Seeler R: Interaction of iron deficiency and lead and the hematologic findings in children with severe lead poisoning. Pediatrics 81:247, 1988.

White JM, Selhi HS: Lead and the red cell. Br J Haematol 30:133, 1975.

Jensen WN, Moreno GD, Bessis MC: An electron microscopic description of basophilic stippling in red cells. Johns Hopkins Med J 25:933, 1965.

Berlin CMJ: Lead poisoning in children. Curr Opin Pediatr 9:173, 1997.

Miller AL: Dimercaptosuccinic acid (DMSA), a non-toxic, water-soluble treatment for heavy metal toxicity. Altern Med Rev 3:199, 1998.

Klein WJ Jr, Metz EN, Price AR: Acute copper intoxication. A hazard of hemodialysis. Arch Intern Med 129:578, 1972.

Manzler AD, Schreiner AW: Copper-induced acute hemolytic anemia. A new complication of hemodialysis. Ann Intern Med 73:409, 1970.

McIntyre N, Clink HM, Levi AJ, Cumings JN, Sherlock S: Hemolytic anemia in Wilson’s disease. N Engl J Med 276:439, 1967.

Deiss A, Lee GR, Cartwright GE: Hemolytic anemia in Wilson’s disease. Ann Intern Med 73:413, 1970.

Hansen PB: Wilson’s disease presenting with severe haemolytic anaemia. Ugeskr Laeger 150:1229, 1988.

Shimono N, Ishibashi H, Ikematsu H, et al: Fulminant hepatic failure during perinatal period in a pregnant woman with Wilson’s disease. Gastroenterol Jpn 26:69, 1991.

Jain S, Nur AM, Ghosh K: Acute hemolytic anemia and biliary colic as presenting manifestations of Wilson’s disease. Am J Gastroenterol 85:476, 1990.

Fairbanks VF: Copper sulfate-induced hemolytic anemia. Arch Intern Med 120:428, 1967.

Blume KG, Hoffbauer RW, Löhr GW, Rüdiger HW: Genetische und biochemische Aspekte der Pyruvatkinase menschlicher Erythrozyten (E.C. Verh Dtsch Ges Inn Med 75:450, 1969.

Boulard M, Blume K, Beutler E: The effect of copper on red cell enzyme activities. J Clin Invest 51:459, 1972.

Kiss JE, Berman D, Van Thiel D: Effective removal of copper by plasma exchange in fulminant Wilson’s disease. Transfusion 38:327, 1998.

Jackson RC, Elder WJ, McDonnell H: Sodium-chlorate poisoning complicated by acute renal failure. Lancet 2:1381, 1961.

Eaton JW, Kolpin CF, Swofford HS, Kjellstrand CM, Jacob HS: Chlorinated urban water: A cause of dialysis-induced hemolytic anemia. Science 181:463, 1973.

Caterson RJ, Savdie E, Raik E, Coutts D, Mahony JF: Heinz-body haemolysis in haemodialysed patients caused by chloramines in Sydney tap water. Med J Aust 2:367, 1982.

Orringer EP, Mattern WD: Formaldehyde-induced hemolysis during chronic hemodialysis. N Engl J Med 294:1416, 1976.

Lubash GD, Phillips RE, Shields JD, Bonsnes RW: Acute aniline poisoning treated by hemodialysis. Arch Intern Med 114:530, 1964.

Lowenstein L, Ballew DH: Fatal acute haemolytic anaemia, thrombocytopenic purpura, nephrosis and hepatitis resulting from ingestion of a compound containing apiol. Can Med Assoc J 78:195, 1958.

Schroder C, Kruger E, Abel J: Acute poisoning caused by the herbicide dichlorprop (preparation SYS 67 PROP). Kinderarztl Prax 59:81, 1991.

Martin H, Woerner W, Rittmeister B: Hämolytische Anämie durch Inhalation von Hydroxylaminen. Klin Wochenschr 42:725, 1964.

Fisher B: The significance of Heinz bodies in anemias of obscure etiology. Am J Med Sci 143, 1955.

Nierenberg DW, Horowitz MB, Harris KM, James DH: Mineral spirits inhalation associated with hemolysis, pulmonary edema, and ventricular fibrillation. Arch Intern Med 151:1437, 1991.

Hunter D: Industrial toxicology. Q J Med 12:185, 1943.

Gasser VC: Perakute hämolytische Innenkörperanamie mit Methämoglobinamie nach Behandlung eines Säuglingsekzems mit Resorcin. Helv Paediatr Acta 9:285, 1954.

Brandes JC, Bufill JA, Pisciotta AV: Amyl nitrite-induced hemolytic anemia. Am J Med 86:252, 1989.

Pugh JI, Enderby GEH: Haemoglobinuria after intravenous myanesin. Lancet 2:387, 1947.

Poinsot J, Guillois B, Margis D, et al: Neonatal hemolytic anemia after intra-amniotic injection of methylene blue. Arch Fr Pediatr 45:657, 1988.

Sills MR, Zinkham WH: Methylene blue-induced Heinz body hemolytic anemia. Am J Dis Child 148:306, 1994.

Davidson S, Seldon M, Jones B: Omeprazole and Heinz-body haemolytic anaemia. Aust N Z J Med 27:441, 1997.

Hassan AB, Seligmann H, Bassan HM: Intravascular hemolysis induced by pentachlorophenol. BMJ 291:21, 1985.

Adams JG, Heller P, Abramson RK, Vaithianathan T: Sulfonamide-induced hemolytic anemia and hemoglobin Hasharon. Arch Intern Med 137:1449, 1977.

Greenberg MS: Heinz body hemolytic anemia. Arch Intern Med 136:153, 1976.

Kaplinsky N, Frankl O: Salicylazosulphapyridine-induced Heinz body anemia. Acta Haematol (Basel) 59:310, 1978.

Ward PCJ, Schwartz BS, White JG: Heinz-body anemia: “Bite cell” variant—A light and electron microscopic study. Am J Hematol 15:135, 1983.

Yoo D, Lessin LS: Drug-associated “bite cell” hemolytic anemia. Am J Med 92:243, 1992.

Landsteiner EK, Finch CA: Haemoglobinuria after intravenous myanesin. N Engl J Med 237:310, 1947.

Rath CE: Drowning hemoglobinuria. Blood 8:1099, 1953.

Tavassoli M: Anemia of spaceflight. Blood 60:1059, 1982.

Mengel CE, Kann HE Jr, Heyman A, Metz E: Effects of in vivo hyperoxia on erythrocytes. II. Hemolysis in a human after exposure to oxygen under high pressure. Blood 25:822, 1965.

Dacie JV: The Haemolytic Anaemias. Grune & Stratton, New York, 1967.

Monzon C, Miles J: Hemolytic anemia following a wasp sting. J Pediatr 96:1039, 1980.

Schulte KL, Kochen MM: Haemolytic anaemia in an adult after a wasp sting. Lancet 2:478, 1981.

Vachvanichsanong P, Dissaneewate P, Mitarnun W: Non-fatal acute renal failure due to wasp stings in children. Pediatr Nephrol 11:734, 1997.

Nance WE: Hemolytic anemia of necrotic arachnidism. Am J Med 31:801, 1961.

Madrigal GC, Ercolani RL, Wenzl JE: Toxicity from a bite of the brown spider (Loxosceles Reclusus): skin necrosis, hemolytic anemia, and hemoglobinuria in a nine-year-old child. Clin Pediatr 11:641, 1972.

Chadha JS, Leviav A: Hemolysis, renal failure, and local necrosis following scorpion sting. JAMA 241:1038, 1979.

Barretto OCO, Cardoso JL, De Cillo D: Viscerocutaneous form of loxoscelism and erythrocyte glucose-6-phosphate deficiency. Rev Inst Med trop Sao Paulo 27:264, 1985.

Wasserman GS, Siegel C: Loxoscelism (brown recluse spider bites): A review of the literature. Clin Toxicol 14:353, 1979.

Wright SW, Wrenn KD, Murray L, Seger D: Clinical presentation and outcome of brown recluse spider bite. Ann Emerg Med 30:28, 1997.

Reid HA: Cobra-bites. BMJ 2:540, 1964.

Gillissen A, Theakston RD, Barth J, et al: Neurotoxicity, haemostatic disturbances and haemolytic anaemia after a bite by a Tunisian saw-scaled or carpet viper (Echis ‘pyramidum’-complex): failure of antivenom treatment. Toxicon 32:937, 1994.

Ham TH, Shen SC, Fleming EM, Castle WB: Studies on the destruction of red blood cells. IV. Blood 3:373, 1948.

Wagner HN, Jr., Razzak MA, Gaertner RA, Caine WP, Jr., Feagin OT: Removal of erythrocytes from the circulation. Arch Intern Med 110:90, 1962.

Shen SC, Ham TH, Fleming EM: Studies on the destruction of red blood cells. III. Mechanism and complications of hemoglobinuria in patients with thermal burns: Spherocytosis and increased osmotic fragility of red blood cells. N Engl J Med 229:701, 1943.

Topley E, Bull JP, Maycock WDA, Mourant AE, Parkin D: The relation of the isoagglutinins in pooled plasma to the haemolytic anaemia of burns. J Clin Pathol 16:79, 1963.

Stohlman F, Jr., Brecher G, Schneiderman M, Cronkite EP: The hemolytic effect of ionizing radiations and its relationship to the hemorrhagic phase of radiation injury. Blood 12:1061, 1957.

Jin YS, Anderson G, Mintz PD: Effects of gamma irradiation on red cells from donors with sickle cell trait. Transfusion 37:804, 1997.
Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology



Etiology and Pathogenesis

March Hemoglobinuria

Sports Anemia

Space Anemia
Clinical and Laboratory Features
Differential Diagnosis
Therapy, Course, and Prognosis
Chapter References

Strenuous activities may cause traumatic damage to red cells, with subsequent hemolysis and hemoglobinuria or metabolic changes leading to an expanded plasma volume and dilution anemia. In astronauts, the effect of microgravity leads to changes in blood volume, with relative erythrocytosis when in space and mild anemia after reentry to Earth’s gravitational field.

Individuals involved in strenuous physical activities and astronauts following spaceflights are frequently found to be mildly anemic.1,2 and 3 The causes are complex and controversial but appear to involve hemolysis and blood loss as well as induced alterations in plasma volume and red cell mass. In marchers and runners, traumatic hemolysis may cause hemoglobinuria and anemia, while in athletes and astronauts, a change in blood volume appears to be the major cause.
The first clue to the pathogenesis of hemoglobinuria and anemia in individuals participating in long marches was provided in 1861 by an army physician who studied a young German soldier who had complained of passing dark urine following strenuous field marches.4 He found that the urine contained hemoglobin and that the condition clearly differed from the well-described paroxysmal hemoglobinuria due to cold. During the next 80 years, many additional cases of hemoglobinuria following long-distance running were reported,5,6 but it was not until 1964 that Davidson provided a logical explanation.7 He noticed that two track runners who complained of dark urine after games had a particularly forceful stamping gait, and he proposed that red cells were destroyed in the soles of the feet during running. After some ingenious preparatory studies the runners were encouraged to change their stride and especially to wear soft linings in their shoes, and the hemoglobinuria disappeared. The beneficial effect of better footwear has been noticed in many subsequent studies of athletes,8 but even with well-designed, padded insoles there is still some traumatic disruption of red cells by pressure on the soles during running and walking.9 Similar traumatic red cell destruction with hemoglobinuria has been reported after beating the head against a wall,10 hand-strengthening exercises in a practitioner of karate,11 and playing the conga drums.12
The effects of intravascular hemolysis on hemoglobin concentration in athletes may be augmented by gastrointestinal blood loss, which occurs in about 20 percent of long-distance runners during strenuous races13,14 and by occasional traumatic renal blood loss.15 These effects, however, should be easily compensated for by healthy individuals and would not be expected to cause a measurable anemia.16 Furthermore, hemoglobinuria and gastrointestinal blood loss have only been observed in runners, not in swimmers or bicyclists, and those endurance athletes also have a reduction in hemoglobin concentration.17 It is also unlikely that the associated loss of iron would result in an iron-deficiency state. Nevertheless, the serum ferritin has been found to be decreased in many studies of athletes in training.18,19 and 20 The cause is obscure but may indicate a greater than anticipated loss of iron in sweat21 or even the rapid turnover of iron-containing compounds active in muscular oxidative metabolism.22 It could also be caused by a shift of iron from tissues to the red cell mass if, despite the slight anemia, there is an increase in the size of the red cell mass. That this may actually be the case is suggested by measurements of the red cell and plasma volumes in athletes in active training.23 It appears that elite runners have an increase in both plasma volume and red cell mass,24,25 and 26 but the gain in plasma volume always exceeds the gain in red cell mass. The results should in theory be of considerable benefit, since the circulatory advantage of an increased red cell mass and blood volume are augmented by an increase in blood fluidity.27
Astronauts are moderately anemic when tested several days after reentry. The cause of this anemia has been related to the redistribution of blood volume that occurs during weightlessness.28 At blast-off, there is acute redistribution of blood from the extremities to the torso, resulting in an acute hypervolemia in the upper part of the body. This induces a diuretic response, which reduces the plasma volume and local hypervolemia but results in an increase in the hematocrit. This causes a reduction in the erythropoietin level and the rate of red cell production. After 8 to 10 days in space, the red cell mass is reduced by 10 to 15 percent, and the astronaut will continue the flight with a normal hematocrit but a reduced red cell mass. At reentry into a normal gravitational field, the plasma and blood volumes are restored rapidly to normal, but the hematocrit, now reflecting the low red cell mass, decreases until an increase in the rate of red cell production restores both hematocrit and red cell mass to normal.
The relatively rapid changes in the size of the red cell mass in space and after reentry have been difficult to explain, since erythrokinetic studies have failed to show dramatic changes in iron turnover or erythropoietin titers.29 The absence of overt hemolysis of red cells labeled by 51Cr before the spaceflight has led to the hypothesis that newly created red cells depend on erythropoietin for their survival and will be selectively destroyed during spaceflight.30 However, the lack of marked changes in erythropoietin levels during and after space-flight fail to explain both the traditional and the new explanation for the acute changes in red cell mass.
In march hemoglobinuria and sports anemia, traumatic hemolysis and blood loss play a role in the mild reduction in the hemoglobin concentration; the anemia is usually associated with a slight increase in reticulocyte count and occasionally the presence of echinocytes.31 Immediately after a period of physical exertion, the urine may contain hemoglobin, hemoglobin casts, and hemosiderin. Serum iron and iron-binding capacity are usually normal, but the ferritin may be lower than before the physical exertion. In space anemias, the only finding is a moderate lowering of hemoglobin and hematocrit for a few weeks after reentry.
The history is, of course, of primary importance and leaves little to the imagination. Nevertheless, a reduction in hemoglobin in any young, healthy individual should be investigated further if not easily explained by the history.
The widespread use by athletes of erythropoietin to augment hemoglobin concentration and in turn oxygen transport to muscles has been difficult to diagnose. However, a high hematocrit in a competing athlete should raise suspicion of such misuse, since intense training would tend to lower the hematocrit.
No treatment is necessary, but if hemolysis is severe enough to cause hemoglobinuria, good footwear and a reduction in physical activities may be recommended.

Londemann R: Low hematocrits during basic training: athlete’s anemia. N Engl J Med 299:1191, 1978.

Eichner ER: The anemias of athletes. Phys Sports Med 14:122, 1986.

Leach CS, Johnson PC: Influence of spaceflight on erythrokinetics in man. Science 225:216, 1984.

Fleischer R: Uber eine neue Form von Hämoglobinurie beim Menschen. Berlin Klin Wochenschr 18:691, 1881.

Gilligan DR, Blumgart HL: March hemoglobinuria: studies of the clinical characteristics, blood metabolism and mechanisms with observations on three new cases and review of literature. Medicine (Baltimore) 20:314, 1941.

Gilligan DR, Altschule MD, Katersky EM: Psychologic intravascular hemolysis of exercise: hemoglobinemia and hemoglobinuria following cross-country runs. J Clin Invest 22:859, 1943.

Davidson RJL: Exertional hemoglobinuria: a report on three cases with studies on the haemolytic mechanism. J Clin Pathol 17:536, 1964.

Buckle RM: Exertional (march) hemoglobinuria: reduction of haemolytic episodes by use of sorbo-rubber insoles in shoes. Lancet 1:1136, 1965.

Eichner ER: Runner’s macrocytosis: a clue to footstrike hemolysis. Runner’s anemia as a benefit versus runner’s hemolysis as a detriment. Am J Med 78:321, 1985.

Ensor CW, Barnett JOW: Paroxysmal hemoglobinuria of traumatic origin. Med-Chir Trans 86:165, 1903.

Streeton JA: Traumatic haemoglobinuria caused by karate exercises. Lancet 2:191, 1967.

Furie B, Penn AS: Pigmenturia from conga drumming: hemoglobinuria and myoglobinuria. Ann Intern Med 80:727, 1974.

Buckman MT: Gastrointestinal bleeding in long distance runners. Ann Intern Med 101:127, 1984.

Mechrefe A, Wexler B, Feller E: Sports anemia and gastrointestinal bleeding in endurance athletes. Med Health 80:216, 1997.

Abarbanel J, Benet AE, Lask D, Kimche D: Sports hematuria. J Urol 143:887, 1990.

Hallberg L, Magnusson B: The etiology of “sports anemia.” Acta Med Scand 216:145, 1984.

Clement DB, Asmundson RC, Medhurst CW: Hemoglobin values: comparative study of the 1976 Canadian Olympic Team. Can Med Assoc J 117:614, 1977.

Magnuson B, Hallberg L, Rossander L, Swolin B: Iron metabolism and “sports anemia”: I and II. Acta Med Scand 216:149, 1984.

Newhouse J, Clement D: Iron status in athletes: an update. Sports Med 5:337,1988.

Roberts D, Smith DJ: Training at moderate altitude: iron status of elite male swimmers. J Lab Clin Med 120:387, 1992.

Pauley P, Jordal R, Strandberg Pedersen N: Dermal excretion of iron in intensely training athletes. Clin Chem Acta 127:19, 1983.

Holloszy J, Coyle EF: Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol 56:831, 1984.

Fellmann N: Hormonal and plasma volume alterations following endurance exercise. Sports Med 13:37, 1992.

Brotherhood J, Brogovic B, Pugh LGC: Haematological status of middle- and long-distance runners. Clin Sci Mol Med 48:139, 1975.

Dressendorfer RH, Wade CE, Amsterdam EA: Development of pseudoanemia in marathon runners during a 20-day road race. JAMA 246:1215, 1981.

Schmidt W, Maasen N, Trost R, Boening D: Training-induced effects on blood volume, erythrocyte turnover, and hemoglobin oxygen properties. Eur J Appl Physiol 57:490, 1988.

Thorling EB, Erslev AJ: The “tissue” tension of oxygen and its relation to hematocrit and erythropoiesis. Blood 31:332, 1968.

Udden MM, Driscoll TB, Pickett MH, Leach-Huntoon CS, Alfrey CP: Decreased production of red blood cells in human subjects exposed to microgravity. J Lab Clin Med 125:442, 1995.

Alfrey CP, Udden MM, Leach-Huntoon C, Driscoll T, Pickett MH: Control of the red blood cell mass in spaceflight. J Appl Physiol 81:98, 1996.

Alfrey CP, Rice L, Udden MM, Driscoll TB: Neocytosis: physiological down-regulator of red-cell mass. Lancet 349:1389, 1997.

Selby GB, Frame DC, Eichner LK, Eichner ER: Athlete’s echinocytes: new cause of exertional hemolysis? Blood 70(suppl):56a, 1987.
Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology



Etiology and Pathogenesis

Underlying Disorders




Localized Vascular Abnormalities
Clinical Features
Laboratory Findings
Differential Diagnosis
Therapy, Course, and Prognosis
Chapter References

The term microangiopathic hemolytic anemia refers to a group of clinical disorders characterized by the fragmentation of red cells as they pass through the platelet-fibrin mesh present in microthrombi which are deposited in capillaries and arterioles. Since platelet-fibrin clot deposition in the small vessels is the main pathogenic mechanism, this disorder has also been referred to as thrombotic microangiopathy. The formation of arteriolar microthrombi can be caused by a variety of mechanisms, including activation of the coagulation system as occurs in disseminated intravascular coagulation, or by the formation of platelet aggregates induced by the release of very large von Willebrand factor multimers as in thrombotic thrombocytopenic purpura (TTP). In addition, antineoplastic and immunosuppressive agents as well as radiation therapy and bacterial toxins may induce endothelial cell injury leading to the formation of microthrombi in the affected vessels. Identification of the microangiopathic process and its specific etiology can help the clinician to institute prompt and appropriate treatment that frequently improves the hemolytic process and reverses end-organ failure.

Microangiopathic hemolytic anemia, first described in 1962,1 refers to a group of clinical disorders that are characterized by fragmentation of the red cells within the circulatory system, leading to intravascular hemolysis. The common pathogenic mechanism is extracorpuscular and involves red cell fragmentation as a result of passage of the red cell through abnormal arterioles. Since deposition of platelets and fibrin is the most frequent cause of the microvascular lesion, this type of anemia has also been named thrombotic microangiopathic hemolytic anemia2 or simply thrombotic microangiopathy.2,3
Thrombus formation inside blood vessels can play a major role in the disruption of red cells, as it can be directly observed when the red cells are forced through a loose fibrin clot formed inside a slide chamber.4 The cells, after attaching to the fibrin, fold around the strands and are either released or fragmented by the force of the flowing blood. Some of the cell fragments reseal their membranes and acquire different shapes that are dependent upon the position and plane in which the red cell attaches and upon the distribution of membrane and hemoglobin within each fragment (Fig. 51-1). Fragmentation of the red cells induced by shear stress from interaction with platelet-fibrin deposits in the vascular bed may not be the only explanation. It is also possible that young erythrocytes may attach to endothelial cells via the association of red cell integrins with endothelial cells expressing adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1).5 Other mechanisms for the attachment of red cells to the endothelium may include the interaction of large von Willebrand factor multimers as bridges between integrins present in the membrane of both young red cells and endothelial cells.6 The attached red cells are then fragmented by the high shear stress present in microvessels. In vivo studies have also demonstrated the role of fibrin in the pathogenesis of microangiopathic hemolytic anemia. For example, snake venoms injected into rabbits induce a rapid defibrination syndrome that is associated with morphological alterations of the red cell, hemoglobinemia, and thrombus formation in several organs. The degree of hemoglobinemia correlates with the intensity of defibrination, and the hemolytic process is aggravated by treating the rabbits with fibrinolytic inhibitors.7 Injection of endotoxin or thrombin into rabbits can also lead to intravascular coagulation with thrombosis of the renal vascular bed, resulting in the fragmentation of the red cells and intravascular hemolysis.8 This experimental model resembles the microangiopathic hemolytic anemia and vascular occlusion found in some patients with sepsis, mainly induced by gram-negative bacteria,9 or purpura fulminans.10 Gastrointestinal infections with Shigella dysenteria or with Escherichia coli, mainly the serotype E. coli O157:H7, can induce a syndrome which is similar to either the uremic hemolytic syndrome or thrombotic thrombocytopenic purpura. Both Shigella and E. coli produce exotoxins that cause endothelial cell injury and platelet-fibrin microthrombi formation.11,12 Microangiopathic hemolysis due to thrombotic thrombocytopenic purpura and uremic hemolytic syndrome is also associated with HIV infection, and the clinical and hematological manifestations of this group of patients respond as well to plasma exchange as non-HIV infected individuals.13,14

FIGURE 51-1 Hanged red cell. Dense fibrin band in background was formed from accumulations of finer strands, some of which are still evident. It is only these denser, more amorphous structures that typically persist postmortem. ×5200 in vitro model, scanning electron microscope. [From BS Bull, Kuhn IN: The production of schistocytes by fibrin strands (a scanning electron microscope study). Blood 35:104, 1970, with permission.]

Patients with invasive carcinoma may have a microangiopathic hemolytic anemia as described in one of the first reports of this syndrome.1 It occurs in approximately 5 percent of cases, and its presence in patients with cancer suggests the presence of disseminated disease.15,16 and 17 Thrombocytopenia, leukocytosis, with a shift to the left, and nucleated red blood cells in the blood film may also be present in this group of patients. The hemolytic process is most likely caused by fibrin deposition inside the blood vessels, but vascular disruption by malignant cells and secretion of cytokines that cause endothelial cell injury may also play a role.15,16 and 17 In some instances, the diagnosis of intravascular coagulation can be made by finding a decrease in the concentration of specific clotting factors and detection of fibrin degradation products (see Chap. 126).16 Mucin-producing tumors are more frequently associated with intravascular coagulation,16 possibly due to the release of tissue factor and of a cysteine protease that is capable of activating factor X directly.18
Intravascular hemolysis can accompany certain complications of pregnancy, most notably preeclampsia, eclampsia, and abruptio placentae.19,20 Intravascular coagulation is thought to play a role in the pathogenesis of the hemolytic process present in preeclampsia and eclampsia. This is supported by the presence of a small number of schistocytes, thrombocytopenia, high levels of fibrinopeptide A, and the deposition of fibrin in the kidney and liver.19,20 and 21 These manifestations are most prominent in a subset of patients with severe preeclampsia, known as the HELLP syndrome, which is characterized by hemolysis, elevated liver enzymes, and low platelets.19,22 However, hemolysis due to red cell fragmentation is also associated with malignant hypertension,1 and it is possible that the severe hypertension which occurs in most of these patients contributes to the disruption of the red cell. The cause of the hemolysis is obscure, but narrowing and hardening of the arterioles along with endothelial cell swelling probably contributes to the mechanical destruction of the erythrocyte. Moreover, hemolysis may subside following normalization of the blood pressure.23
Two related clinical entities, thrombotic thrombocytopenic purpura and uremic hemolytic syndrome, are prototypical of microangiopathic hemolysis, which is accompanied by thrombocytopenia and by thrombosis of the small blood vessels of several organs, mainly the central nervous system and/or the kidneys24 (see Chap. 117). Moreover, these microthrombi are mainly formed by platelet aggregates containing small amounts of fibrin(ogen).25 In TTP the platelet thrombi appear to be formed by the binding of large multimers of von Willebrand factor to platelets under high shear stress.26,27
Certain drugs, especially antineoplastic agents, can cause clinical disorders that resemble uremic hemolytic syndrome or, less frequently, thrombotic thrombocytopenic purpura17,28 (see Chap. 117). Mitomycin, given alone or in combination with other agents, is the drug most frequently associated with this disorder. However, bleomycin, daunorubicin in combination with cytosine arabinoside, and regimens containing cisplatin also have been implicated.17,28 The clinical manifestations of uremic hemolytic syndrome following mitomycin therapy frequently do not become apparent until several weeks or months after discontinuation of the drug.17,28 Although the pathogenesis of the hemolytic uremic syndrome is unclear, in some patients the disease is stable while in others the malignant process is in remission at the time of diagnosis, suggesting that mitomycin is, at least in part, responsible for the hematological abnormalities and for the lesions seen in the kidneys.17,28 It is unclear whether mitomycin directly induces endothelial damage of the renal vascular bed or the lesions are induced by the deposition of immune complexes.17 The pathological lesions consist of arteriolar microthrombi similar to those described in idiopathic uremic hemolytic syndrome, and these patients frequently die from renal failure.17,28 The recognition of this entity is important, since these patients can develop severe complications following the transfusion of blood products, whereas they may improve following extracorporeal immunoadsorption of their plasma on columns of staphyloccocal protein A.28,29 Paradoxically, ticlopidine, a drug that inhibits platelet function, can cause severe thrombotic thrombocytopenic purpura leading to the demise of about one-third of the affected individuals.30,31 The mechanism by which ticlopidine, or one of its metabolites, induces the thrombotic disorder is unknown, but the early recognition of this disorder is important, since plasma exchange reduces the mortality substantially.31
Patients who have undergone kidney or liver transplantation occasionally develop microangiopathic hemolysis, thrombocytopenia, and impaired kidney function.32 Multiple pathogenic mechanisms may be involved in this group of patients, including vascular damage induced by tissue rejection, the formation of immune complexes, and immunosuppressive therapy. These factors may lead to the formation of microthrombi in the small vessels of the kidney.32,33 Among the immunosuppressive agents, cyclosporine is the drug most frequently associated with the hemolytic syndrome in this group of patients, and reduction of the dose or discontinuation of the drug followed by plasma exchange can reverse this pathologic process.34,35 Hemolytic uremic syndrome can also occur after allogeneic and autologous marrow transplants, and it seems that total body irradiation, rather than chemotherapy, given to ablate the bone marrow is the responsible agent for the appearance of the uremic hemolytic syndrome.32,33
Patients with generalized vasculitis associated with immunological disorders (e.g., systemic lupus erythematosus, polyarteritis nodosa, Wegener’s granulomatosis, and scleroderma) may also develop intravascular hemolysis due to microangiopathic hemolytic anemia.36 The deposition of immune complexes in the arterioles may lead to local activation of the coagulation factors and fibrin formation. Damaged endothelium together with fibrin deposition are responsible for the fragmentation of the red cells.36
Although the majority of cases of microangiopathic hemolytic anemia are due to disorders involving the vascular bed of several organs, occasionally fragmentation of the red cells occurs due to localized vascular abnormalities. Patients with cutaneous cavernous hemangiomas and with hemangioendotheliomas of the liver can sometimes develop microangiopathic hemolytic anemia associated with intravascular coagulation induced by the vascular malformation.37,38
The clinical manifestations of microangiopathic hemolytic anemia are the consequence of the primary process and may also reflect the organ affected by the intravascular deposition of platelets and fibrin (e.g., neurological manifestations of thrombotic thrombocytopenic purpura). Severe anemia and kidney failure may contribute to the constitutional symptoms in these patients. The physical findings can also reflect those expressed by the clinical entity causing the microangiopathic hemolytic anemia.
The most prominent laboratory findings in microangiopathic hemolytic anemia are the alteration in the shape of the red blood cell, such as helmet cells, and formation of fragments termed schistocytes. Increases in the number of schistocytes to more than 3 per 5000 red cells should be considered abnormal, and a cause for this abnormality should be sought.39 The typical schistocyte can be recognized by the presence of one to three sharp spicules (see Chap. 22). Microspherocytosis is also commonly seen. The alteration in the morphology of the red cell is similar to that seen in traumatic cardiac hemolytic anemia (see Chap. 50 and Fig. 50-1). The reticulocyte count is usually elevated, while the degree of thrombocytopenia is variable depending on the intensity of the consumption of platelets and on the capacity of the bone marrow to compensate for this process.
Another pertinent laboratory finding is a decrease in the concentration of haptoglobin, and some patients with marked hemolysis also have increased levels of plasma hemoglobin and hemoglobinuria. High levels of lactic dehydrogenase is almost a constant finding in microangiopathic hemolysis, and the level of this enzyme correlates with the activity of the disease. Coagulation abnormalities due to consumption coagulopathy can be seen in this group of patients. In patients with overt disseminated intravascular coagulation, factors V, VIII, antithrombin III, and fibrinogen are usually depleted. In addition, the levels of fibrinogen and fibrin degradation products are elevated, reflecting increased fibrinolytic activity. In other patients, the coagulation abnormalities are rather subtle, and immunological assays of fibrinopeptide A or of fibrin D dimer are useful in establishing the diagnosis. In several of the clinical entities associated with microangiopathic hemolysis like TTP, the formation of microthrombi is mainly due to platelet aggregates rather than fibrin deposition secondary to the activation of the coagulation system, and these cases show minimal or no evidence of intravascular coagulation.24,25
Microangiopathic hemolytic anemia should be differentiated from other types of intravascular hemolysis, for example, certain forms of autoimmune hemolytic anemia or paroxysmal nocturnal hemoglobinuria. However, the presence of schistocytes in the blood film, thrombocytopenia, negative Coombs’ test combined with the detection of intravascular coagulation, and identification of the primary process are characteristic of microangiopathic hemolytic anemia. The causes of the anemia can be multifactorial; iron and/or folate deficiency, hemorrhage, and marrow involvement due to infiltrative processes can contribute to the anemia. The most common causes of microangiopathic hemolytic anemia are listed in Table 51-1.


The treatment of this disorder should be directed toward the management of the underlying process that is responsible for the microangiopathic hemolysis. Frequently, patients require red cell transfusions to maintain an adequate level of hemoglobin. In cases presenting bleeding manifestations and thrombocytopenia, platelet transfusions can help to arrest the bleeding. The clinical management of thrombotic thrombocytopenic purpura and uremic hemolytic syndrome is discussed in detail in Chap. 117.
Although intravascular coagulation is commonly a pathogenic mechanism in microangiopathic hemolytic anemia, the use of anticoagulants is controversial. In a few selected cases, heparin therapy seems to improve this process,40 but the use of anticoagulants does not seem to be efficacious in the majority of patients40 (Chap. 126). In the particular case of uremic hemolytic syndrome associated with mitomycin C, immunoadsorption of patient plasma by staphylococcal protein A can normalize the platelet count and stabilize the serum creatinine.29

Brain MC, Dacie JV, Hourihane DO: Microangiopathic haemolytic anaemia: the possible role of vascular lesions in pathogenesis. Br J Haematol 8:358, 1962.

Symmers WC: Thrombotic microangiopathic haemolytic anaemia. Br Med J 2:897, 1952.

Kwaan HC: Introduction: thrombotic microangiopathy. Semin Hematol 24:69, 1987.

Bull BS, Rubenberg ML, Dacie JV, Brain MC: Microangiopathic haemolytic anaemia: mechanisms of red cell fragmentation in vitro studies. Br J Haematol 14:643, 1968.

Swerlick RA, Eckman JR, Kumar A, Jeitler M, Wick TM: a4b1-integrin expression on sickle reticulocytes: vascular cell adhesion molecule-1-dependent binding to endothelium. Blood 82:1891, 1993.

Wick TM, Moake JL, Udden MM, McIntire LV: Unusually large von Willebrand factor multimers preferentially promote young sickle and nonsickle erythrocyte adhesion to endothelial cells. Am J Haematol 42:284, 1993.

Rubenberg ML, Regoeczi E, Bull BS, Dacie JV, Brain MC: Microangiopathic haemolytic anaemia: the experimental production of haemolysis and red cell fragmentation by defibrination in vivo. Br J Haematol 14:627, 1968.

Brain MC: Microangiopathic hemolytic anemia. Ann Rev Med 21:133, 1970.

Kreger BE, Craven DE, McCabe WR: Gram-negative bacteremia: IV. Re-evaluation of clinical features and treatment in 612 patients. Am J Med 68:344, 1980.

Hollingsworth JH, Mohler DN: Microangiopathic hemolytic anaemia caused by purpura fulminans. Ann Intern Med 68:1310, 1968.

Keusch GT, Acheson DWK: Thrombotic thrombocytopenic purpura associated with Shiga toxins. Semin Hematol 34:106, 1997.

Boyce TG, Swerdlow DL, Griffin PM: Escherichia coli O157:H7 and the hemolytic-uremic syndrome. N Engl J Med 333:364, 1995.

Thompson CE, Damon LE, Ries CA, Linker CA: Thrombotic microangiopathies in the 1980s: clinical features, response to treatment, and the impact of the human immunodeficiency virus epidemic. Blood 80:1890, 1992.

Hymes KB, Karpatkin S: Human immunodeficiency virus infection and thrombotic microangiopathy. Semin Hematol 34:117, 1997.

Antman KH, Skarin AT, Mayer RJ, Hargreaves HK, Canellos GP: Microangiopathic hemolytic anemia and cancer: a review. Medicine 58:377, 1979.

Murgo AJ: Thrombotic microangiopathy in the cancer patient including those induced by chemotherapeutic agents. Semin Hematol 24:161, 1987.

Gordon LI, Kwaan HC: Cancer- and drug-associated thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Semin Hematol 34:140, 1997.

Rickles FR, Edwards RL: Activation of blood coagulation in cancer: Trousseau’s syndrome revisited. Blood 62:14, 1983.

McCrae KR, Cines DB: Thrombotic microangiopathy during pregnancy. Semin Hematol 34:148, 1997.

Pritchard JA, Brekken AL: Clinical and laboratory studies on severe abruptio placentae. Am J Obstet Gynecol 97:681, 1967.

Vassalli P, Morris RH, McCluskey RT: The pathogenic role of fibrin deposition in the glomerular lesions of toxemia of pregnancy. J Exp Med 118:467, 1963.

Weinstein L: Syndrome of hemolysis, elevated liver enzymes, and low platelet count: a severe consequence of hypertension in pregnancy. Am J Obstet Gynecol 142:159, 1982.

Capelli JP, Wesson LG Jr, Erslev AJ: Malignant hypertension and red cell fragmentation syndrome. Ann Intern Med 64:128, 1966.

Kwaan HC: Clinicopathologic features of thrombotic thrombocytopenic purpura. Semin Hematol 24:71, 1987.

Asada Y, Sumiyoshi A, Hayashi T: Immunohistochemistry of the vascular lesion in thrombotic thrombocytopenic purpura, with special reference to factor VIII related antigen. Thromb Res 38:469, 1985.

Tsai H-M, Lian E C-Y: Antibodies to von Willebrand factor-cleaving protease in acute thrombotic thrombocytopenic purpura. N Engl J Med 339:1585, 1998.

Furlan M, Robles R, Galbusera M, et al: von Willebrand factor-cleaving protease in thrombotic thrombocytopenia purpura and the hemolytic-uremic syndrome. N Engl J Med 339:1578, 1998.

Doll DC, Yarbro JW: Vascular toxicity associated with antineoplastic agents. Semin Oncol 19:580, 1992.

Snyder HW Jr, Mittelman A, Oral A, et al: Treatment of cancer chemotherapy-associated thrombotic thrombocytopenic purpura/hemolytic uremic syndrome by protein A immunoadsorption of plasma. Cancer 71:1882, 1993.

Page Y, Tardy B, Zeni F, Comtet C, Terrana R, Bertrand JG: Thrombotic thrombocytopenic purpura related to ticlopidine. Lancet 337:774, 1991.

Bennett CL, Weinberg PD, Rozenberg-Ben-Dror K, Yarnold PR, Kwaan HC, Green G: Thrombotic thrombocytopenic purpura associated with ticlopidine: a review of 60 cases. Ann Int Med 128:541, 1998.

Schriber JR, Herzig GP: Transplantation-associated thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Semin Hematol 34:126, 1997.

Rabinowe SN, Soiffer RJ, Tarbell NJ, et al: Hemolytic-uremic syndrome following bone marrow transplantation in adults for hematologic malignancies. Blood 77:1837, 1991.

Buturovic J, Kandus A, Malovrh M, Bren A, Drinovec J: Cyclosporine-associated hemolytic uremic syndrome in four renal allograft recipients: resolution without specific therapy. Transplant Proc 22:1726, 1990.

Venkat KK, Tkach D, Kupin W, et al: Reversal of cyclosporine-associated hemolytic-uremic syndrome by plasma exchange with fresh-frozen plasma replacement in renal transplant recipients. Transplant Proc 23:1256, 1991.

Kwaan HC: Miscellaneous secondary thrombotic microangiopathy. Semin Hematol 24:141, 1987.

Propp RP, Scharfmann WB: Hemangioma-thrombocytopenia syndrome associated with microangiopathic hemolytic anemia. Blood 28:623, 1966.

Alpert LI, Benisch G: Hemangioendothelioma of the liver associated with microangiopathic hemolytic anemia. Am J Med 48:624, 1970.

Chou C, Jajeh A, Shiomoto G, Shah P: Schistocytes in normal individuals. Blood 92:4b, 1998.

Feinstein DI: Diagnosis and management of disseminated intravascular coagulation: the role of heparin therapy. Blood 60:284, 1982.
Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology


Etiology and Pathogenesis
Clinical Features
Laboratory Features
Differential Diagnosis
Therapy, Course, and Prognosis
Chapter References

The abrasive effect on red cells of arteriosclerotic or stenotic cardiac valves is usually minimal, resulting at most in a mild, often compensated hemolytic anemia. However, the introduction of artificial valves was initially associated with marked red cell destruction and the development of an overt hemolytic anemia. Recently, the design of the artificial valves and the use of more compatible plastics or biologic materials have greatly reduced their traumatic effects and minimized hemolysis. Actually, the potential thrombogenic effect of artificial valves far outstrips their destructive effect on red cells, and cardiac hemolytic anemia is now an almost nonexistent problem.

In the 1950s cardiac corrective surgery became possible, and it was almost immediately observed that patients in whose aorta a Hufnagel valve was inserted developed anemia.1 This anemia was shown to be caused by mechanical injury and fragmentation of red cells impacted at high speed on a foreign surface.2,3 Since then the prevention of such injury has been a challenge in the construction of prosthetic valves and surfaces, and successful innovations have led to a decreased incidence of valve-related traumatic cardiac hemolytic anemia. Currently, hemolytic anemia is considered a minor complication in reviews of large series of patients4,5,6,7 and 8 and is mainly relegated to case reports of patients with old or dysfunctional prosthetic valves.9,10,11,12,13 and 14
In aqueous suspension the red cell membrane can withstand shear-producing stress of up to 15,000 dyne/cm2.15 Such a stress is rarely encountered in vivo, but determination of red cell survival, serum haptoglobin level, and serum lactic dehydrogenase concentration in patients with valvular disorders suggests that some hemolysis takes place. This hemolysis, however, is mild and rarely causes overt hemolytic anemia except in patients with severe aortic16 or subaortic17 stenosis generating pressure gradients across the valve of more than 50 torr.18 The abnormalities that have been found to produce hemolytic anemia are summarized in Table 50-1.


All prosthetic cardiac valves have an orifice size smaller than that of the natural valve, and after implantation this orifice is further reduced by tissue ingrowth and endothelialization.19 The Starr-Edwards cage ball valve has a slightly smaller aperture than the more commonly used tilting disc valve (Bjork-Shiley or St. Jude), but the hemodynamic differences between well-functioning prosthetic valves and natural valves are small. Several complications, however, may cause turbulence in the blood flowing around or through a prosthetic valve and expose the red cells to very high shear stresses. The blood may flow around the valve through openings created by improper positioning or by spontaneous separation of the valve from the annular ring.20,21 It may also flow through a constricted outlet in the Starr-Edwards model because of “ball variance,” in which the plastic ball takes up lipids, swells, and fails to move freely in the cage.22,23
Nevertheless, the turbulence and shear stresses encountered in patients with artificial valves are rarely much higher than those in patients with uncorrected aortic stenosis or mitral regurgitation. Consequently, the severe red cell destruction seen in some patients with artificial valves cannot be caused only by hemodynamic turbulence but requires that this turbulence occur in a space enclosed or bordered by a foreign surface. Studies of red cells in a cone-plate viscosimeter show that hemolysis occurs when shear forces at plastic interfaces exceed 2000 dyne/cm2 (Fig. 50-1).24 Such shear forces are encountered across artificial prosthetic devices that are coated with various plastic compounds or constructed of carbon or metallic material. These coatings are eventually covered by a layer of endothelial cells. Unfortunately, this covering is not firmly bonded to the materials, and if it is denuded, red cells in rapidly flowing blood will become damaged by contact with the artificial surface. This damage will result in mild, usually compensated anemia,25 but severe hemolytic anemia may occur.26 Of more clinical importance is the fact that nonendothelialized surfaces are thrombogenic and may cause platelet activation, thrombus formation, and distant embolization (see Chap. 130). In patients undergoing artificial heart transplantation, the hemolysis, although significant and requiring transfusion replacement, is overshadowed by complications from thrombosis and embolization.27,28 When blood is exposed to foreign surfaces under less turbulent conditions, as in an oxygenator,7 dialysis tubing,29 or endocardiac30 or aortofemoral prostheses,31 hemolysis may occur but is rarely pronounced. In such cases it has been proposed that the hemolysis is due in part to complement activation.32

FIGURE 50-1 (a) Normal human erythrocytes. (b) Human erythrocytes subjected to shearing stress of 2616 dyne/cm2. (c) Erythrocytes from a patient with a hemolytic anemia associated with a malfunctioning prosthetic aortic valve. Each blood film stained with Wright stain. (From Nevaril et al.24)

Largely to overcome these thromboembolic problems, nonthrombogenic bioprosthetic valves have been developed. These can be allographs, derived from human aortic leaflets, or xenographs (Carpenter-Edwards or Hancock’s), derived from porcine aortic leaflets.19 The valvular orifice is slightly smaller than in the ball or disc artificial valve, but overt hemolysis does not occur unless the stitching fails and permits perivalvular leakage.13,14 The valves usually have a potentially thrombogenic Teflon sewing ring, but since it becomes endothelialized within a few months, permanent anticoagulant therapy is not needed. Unfortunately, these valves are less durable than mechanical prosthetic valves and may need replacement 5 to 10 years after insertion.19 In order to limit the need for anticoagulation, bioprosthetic material has been preferred for valve replacement in the elderly, in whom long-term durability may be of lesser concern. In the future such considerations may be less important, since improved design appears to have rendered bioprosthetic valves as durable as mechanical valves.33
The severity of the anemia is highly variable in patients with heart valve prostheses. Mild compensated hemolysis is usually present, but overt anemia is unusual, and only in a rare individual will the anemia be severe enough to require transfusions. However, since patients with cardiac diseases generally have less capacity to adapt to an anemia, even a mild reduction in hemoglobin concentration may cause angina or congestive heart failure.
Even when the hemoglobin level is almost normal, the reticulocyte count is usually elevated, as is the serum lactic acid dehydrogenase activity. Blood films display helmet cells, triangular cells, and other fragmented red cell forms having characteristically sharp points.
The plasma hemoglobin level may be elevated, and the haptoglobin concentration may be diminished, resulting in hemosiderinuria,34 and occasionally there is a significant loss of iron in the urine, with reduced serum ferritin levels and, not uncommonly, with frank iron deficiency.35
The white cell count may be normal or slightly elevated. The platelet count may be decreased, suggesting intravascular consumption of platelets on the foreign surfaces.36
The diagnosis is usually straightforward and is based on the presence of fragmented red cells and evidence of chronic hemolysis in a patient with an artificial valve. The use of transesophageal electrocardiography may be useful in identifying paravalvular regurgitation.37 It is, of course, important to remember that even patients with artificial valves may have unrelated autoimmune or nutritional deficiency anemias.
If the anemia is sufficiently severe, the most effective treatment consists of replacement of the prosthesis. In most cases, however, the anemia is very mild or completely compensated, and it is merely necessary to ensure good erythropoietic activity in order to maintain this compensation. For that purpose it is recommended to replace urinary iron loss with 300 mg/day of ferrous sulfate orally. Folic acid, 1 mg/day, may also be beneficial. Recombinant erythropoietin has also been successful in alleviating the anemia in a few transfusion-dependent patients.38

Ross JC, Hufnagel CA, Fries ED, et al: The hemodynamic alterations produced by plastic valvular prosthesis for severe aortic insufficiency in man. J Clin Invest 33:891, 1954.

Sayed HM, Dacie JV, Handley DA, et al: Haemolytic anaemia of mechanical origin after open heart surgery. Thorax 16:356, 1961.

Marsh GW, Lewis SM: Cardiac haemolytic anaemia. Semin Hematol 6:133, 1969.

Starr A: Ball valve prostheses: a perspective after 22 years, in Advances in Cardiac Valves, edited by ME DeBakey, pp 1–13. Yorke Medical Books, New York, 1983.

DeBakey ME, Lawrie GM, Morris GC, et al: Experience with 366 St. Jude valve prostheses in 346 patients, in Advances in Cardiac Valves, edited by ME DeBakey, pp 14–21. Yorke Medical Books, New York, 1983.

Thompson ME, Lewis JH, Porkolab FL, Hasiba U, Spero JA: Indexes of intravascular hemolysis, quantification of coagulation factors and platelet survival in patients with porcine heterograft valves. Am J Cardiol 51:489, 1983.

Arom K: Aortic valve replacement: long-term results with various mechanical prostheses. Asian Cardiovasc Thorac J 1:39, 1993.

Aoyagi S, Oryoji A, Nishi Y, Tanaka K, Kosuga K, Oishi K: Long-term results of valve replacement with the St. Jude medical valve. J Thorac Cardiovasc Surg 108:1021, 1994.

Schaer DH, Cheng TO, Aaron BL: Hemolytic anemia and acute mitral regurgitation caused by a torn cusp of a porcine mitral prosthetic valve 7 years after its implantation. Am Heart J 113:404, 1987.

Kutsche LM, Alexander JA, VanMierop LH: Hemolytic anemia secondary to erosion of a Silastic band into the lumen of the pulmonary trunk. Am J Cardiol 55:1438, 1985.

Barmada H, Starr A: Clinical hemolysis with the St. Jude heart valve without paravalvular leak. Med Prog Technol 20:191, 1994.

Kihara S, Kasegawa H, Kobayashi N, et al: Severe hemolysis due to artificial chordae displacement. J Heart Valve Dis 6:69, 1997.

Amidon TM, Chou TM, Rankin JS, Ports TA: Mitral and aortic paravalvular leaks with hemolytic anemia. Am Heart J 125:266, 1993.

Formolo JM, Reyes P: Refractory hemolytic anemia secondary to perivalvular leak diagnosed by transesophageal echocardiography. J Clin Ultrasound 23:185, 1995.

Blackshear PL Jr, Dorman FD, Steinbach JH, Maybach EJ, Singh A, Collingham RE: Shear wall interaction and hemolysis. Trans Am Soc Artif Intern Organs 12:113, 1966.

Miller DS, Mengel CE, Kremer WB, et al: Intravascular hemolysis in a patient with valvular heart disease. Ann Intern Med 65:210, 1966.

Solanski DL, Sheikh MU: Fragmentation and hemolysis in idiopathic hypertrophic subaortic stenosis. South Med J 71:599, 1978.

Jacobson AJ, Rath CE, Perloff SK: Intravascular hemolysis and thombocytopenia in left ventricular outflow obstruction. Br Heart J 35:49, 1973.

Braunwald E: Artificial cardiac valves, in Heart Disease, 5th ed, edited by E Braunwald, pp 1061–1076. Saunders, Philadelphia, 1997.

Kastor JA, Akburian M, Buckley MJ: Paravalvular leaks and hemolytic anemia following Starr-Edwards aortic and mitral valves. J Thorac Cardiovasc Surg 56:279, 1968.

Viner ED, Frost W: Hemolytic anemia due to a Teflon aortic valve prosthesis. Ann Intern Med 63:295, 1965.

Eyster E: Traumatic hemolysis with hemoglobinuria due to ball variance. Blood 33:391, 1969.

Stohlman F Jr, Sarnoff SJ, Case RB, Ness AT: Hemolytic syndrome following the insertion of a Lucite ball valve prosthesis into the cardiovascular system. Circulation 13:586, 1956.

Nevaril CG, Lynch EC, Alfrey CP, Hellums JD: Erythrocyte damage and destruction induced by shearing stress. J Lab Clin Med 71:784, 1968.

Brodeur MTH, Sutherland DW, Koler RD, et al: Red blood cell survival in patients with aortic valvular disease and ball valve prostheses. Circulation 32:570, 1965.

Marsh GW: Intravascular haemolytic anemia after aortic-valve replacement. Lancet 2:986, 1964.

Kormos RL, Borovetz HS, Griffith BP, Huns TC: Rheologic abnormalities in patients with the Jarvik-7 total artificial heart. Trans Am Soc Artif Intern Organs 33:413, 1987.

DeVries WC: The permanent artificial heart: four case reports. JAMA 259:849, 1988.

Francos GC, Burke JF Jr, Besarab A, Baumer LH, Paek SU, Sebening F: An unsuspected cause of acute hemolysis during hemodialysis. Trans Am Soc Artif Intern Organs 29:140, 1983.

Sigler AT, Forman EN, Zinkham WH, Neill CA: Severe intravascular hemolysis following surgical repair of endocardial cushion defects. Am J Med 35:407, 1963.

Manny J, Manny N, Abu-Dallo K, et al: Traumatic hemolysis after aortofemoral bypass. Isr J Med Sci 13:50, 1977.

Salama A, Hugo P, Heinrich D, et al: Deposition of terminal C5b-9 complement complexes on erythrocytes and leukocytes during cardiopulmonary bypass. N Engl J Med 318:408, 1988.

Holper K, Wottke M, Lewe T, et al: Bioprosthetic and mechanical valves in the elderly: benefits and risks. Ann Thorac Surg 60:S443, 1995.

Slater SD, Rahman M, Lindsay RM: Renal function in chronic intravascular haemolysis associated with prosthetic cardiac valves. Clin Sci 44:511, 1973.

Heilman E, Bender F, Gulker H, Bonke J: Investigations of iron and folate levels in serum after implantation of heart valve prostheses. Herz 4:298, 1979.

Harker LA, Slichter SJ: Studies of platelet and fibrinogen kinetics in patients with prosthetic heart valves. N Engl J Med 283:1302, 1970.

Garcia MJ, Vandervoort P, Stewart WJ, et al: Mechanisms of hemolysis with mitral prosthetic regurgitation study using transesophageal echocardiography and fluid dynamic simulation. J Am Coll Cardiol 27:399, 1996.

Kornowski R, Schwartz D, Jaffe A, Pines A, Aderka D, Levy Y: Erythropoietin therapy obviates the need for recurrent tranfusions in a patient with severe hemolysis due to prosthetic valves. Chest 102:315, 1992.
Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology



Definition and History
Etiology and Pathogenesis

Toxic Methemoglobinemia

Nadh-Diaphorase Deficiency

Hemoglobins M

Low-Oxygen Affinity Hemoglobins


Mode of Inheritance
Clinical Features
Laboratory Features

Toxic Methemoglobinemia

Nadh-Diaphorase Deficiency

Abnormal Hemoglobins

Differential Diagnosis
Therapy, Course, and Prognosis

Toxic Methemoglobinemia

Hereditary Methemoglobinemia

Chapter References

Cyanosis, blue discoloration of the skin and mucous membranes, is usually due to a change in the color of hemoglobin. Commonly this is due to a high concentration of deoxyhemoglobin because of cardiorespiratory failure or right-to-left shunting. Cyanosis also may indicate that an abnormal hemoglobin is present or that there is an increased concentration of a normally present hemoglobin derivative. Methemoglobin is a reversible oxidation product of hemoglobin and can be present in excess amounts either because of rapid oxidation of hemoglobin by drugs or toxic chemicals or because of a hereditary defect in the methemoglobin-reducing system. Hemoglobins M are mutant hemoglobins that cannot be adequately reduced by the enzymatic systems of the red cell. Sulfhemoglobins are irreversible denaturation products of hemoglobin which can produce cyanosis even when present in relatively low and harmless quantities.
Toxic methemoglobinemia is effectively treated by intravenous infusion of methylene blue, which links the highly efficient NADPH-reducing system to methemoglobin.

Acronyms and abbreviations that appear in this chapter include: G-6-PD, glucose-6-phosphate dehydrogenase.
A bluish discoloration of the skin and mucous membranes, designated cyanosis, has been recognized since antiquity as a manifestation of lung or heart disease. Cyanosis resulting from drug administration has also been recognized since before 1890.1 Toxic methemoglobinemia occurs when various drugs or toxic substances either oxidize hemoglobin directly in the circulation or facilitate its oxidation by molecular oxygen.
In 1912 Sloss and Wybauw reported a case of a patient with idiopathic methemoglobinemia.2 Later Hitzenberger3 suggested that a hereditary form of methemoglobinemia might exist, and subsequently numerous such cases were reported.4 In 1948 Hörlein and Weber5 described a family in which eight members over four generations manifested cyanosis. The absorption spectrum of methemoglobin was abnormal. They demonstrated that the defect must reside in the globin portion of the molecule. Subsequently Singer suggested that such abnormal hemoglobins be given the designation hemoglobin M.6
The existence of abnormal hemoglobins that cause cyanosis through quite another mechanism was first recognized in 1968 with the description of hemoglobin Kansas.7 Here the cyanosis was not due to methemoglobin, as occurs in hemoglobin M, but rather to an abnormally low oxygen affinity of the mutant hemoglobin. Thus, at normal oxygen tensions a large amount of deoxygenated hemoglobin is present in the blood.
The cause of still another form of methemoglobinemia that occurs independently of drug administration and without the existence of any abnormality of the globin portion of hemoglobin was first explained by Gibson,8 who clearly pointed to the site of the enzyme defect, NADH diaphorase.
Sulfhemoglobinemia refers to the presence in the blood of hemoglobin derivatives that are defined by their characteristic absorption of light at 620 nm even in the presence of cyanide.
Methemoglobinemia decreases the oxygen-carrying capacity of blood, because the oxidized iron cannot reversibly bind oxygen. Moreover, when one or more iron atoms have been oxidized, the conformation of hemoglobin is changed so as to increase the oxygen affinity of the remaining ferrous heme groups. In this way methemoglobinemia exerts a dual effect in impairing the supply of oxygen to tissues.9
Hemoglobin is continuously oxidized in vivo from the ferrous to the ferric state. The rate of such oxidation is accelerated by many drugs and toxic chemicals, including sulfonamides, lidocaine and other aniline derivatives, and nitrites. A vast number of chemical substances may cause methemoglobinemia.10,11 and 12 Some of the agents that are responsible for clinically significant methemoglobinemia in current clinical practice are listed in Table 49-1.


NADH diaphorase catalyzes a step in the major pathway for methemoglobin reduction. This enzyme reduces cytochrome b5, using NADH as a hydrogen donor. The reduced cytochrome b5 reduces, in turn, methemoglobin to hemoglobin (see Chap. 26). A steady-state methemoglobin level is achieved when the rate of methemoglobin formation equals the rate of methemoglobin reduction, either through the NADH-diaphorase system or through the relatively minor auxiliary mechanisms such as direct chemical reduction by ascorbate and reduced glutathione. A NADPH-linked enzyme, NADPH diaphorase, does not play a role in methemoglobin reduction except when a linking dye such as methylene blue is supplied (see “Treatment,” below). A marked diminution in the activity of NADH diaphorase will result in the accumulation of the brown pigment in circulating erythrocytes.
Accordingly, hereditary deficiency of the enzyme that reduces cytochrome b5, NADH diaphorase (sometimes designated cytochrome b5 reductase), is one of the causes of methemoglobinemia. A number of mutations of NADH diaphorase have been identified at the nucleotide level.41,42,43,44,45,46,47,48 and 49
Most of the patients with this disorder merely have methemoglobinemia, and these have been classified as having type I disease. In type II disease, deficiency also exists in nonerythroid cells, such as fibroblasts and lymphocytes.50 Patients with this form of disease are afflicted, in addition to methemoglobinemia, with a progressive encephalopathy and with mental retardation. The finding that fatty acid elongation is defective in the platelets and leukocytes of such patients51 may provide a clue to the type of defect that could occur in the central nervous system, where fatty acid elongation plays an important role in myelination. Occasionally patients with deficiency of NADH diaphorase in nonerythroid cells do not suffer any neurologic disorder, and it has been suggested that they be designated as having type III disease.42,52
A combination of both increased hemoglobin oxidation and decreased methemoglobin reduction also may occur. Since the activity of NADH diaphorase is normally low in newborn infants,53 they are particularly susceptible to the development of methemoglobinemia. Thus, serious degrees of methemoglobinemia have been observed in infants as a result of toxic materials, such as aniline dyes used on diapers,54 and the ingestion of nitrate-contaminated water.55 Bacterial action in the intestinal tract may reduce nitrates to nitrites, which in turn cause methemoglobinemia. In rural areas, fatal methemoglobinuria in infants due to wells contaminated with nitrates still occurs.56
Heterozygotes for NADH-diaphorase deficiency are not usually clinically methemoglobinemic. However, under the stress of administration of drugs which normally induce only slight, clinically unimportant, methemoglobinemia such persons may become severely cyanotic because of methemoglobinemia.57
An animal model of NADH-diaphorase deficiency has been described in the cat.58,59 and 60
The molecular mechanisms by which hemoglobin binds oxygen and releases it are discussed in detail in Chapter 28. Heme is held in a hydrophobic “heme pocket” between the E and F a-helices of each of the four globin chains. The iron atom in the heme forms four bonds with the pyrrole nitrogen atoms of the porphyrin ring and a fifth covalent bond with the imidazole nitrogen of a histidine residue in the nearby F a-helix (Fig. 49-1).61 This histidine, residue 87 in the a chain and 92 in the b chain, is designated as the proximal histidine. On the opposite side of the porphyrin ring the iron atom lies adjacent to another histidine residue to which, however, it is not covalently bonded. This distal histidine occupies position 58 in the a chain and position 63 in the b chain. Under normal circumstances oxygen is occasionally discharged from the heme pocket as a superoxide anion, removing an electron from the iron and leaving it in the ferric state. The enzymatic machinery of the red cell efficiently reduces the iron to the divalent form, converting the methemoglobin to hemoglobin (see Chap. 26).

FIGURE 49-1 Diagrammatic representation of the heme group inserted into the heme pocket. A, proximal histidine; B, distal histidine. (a) In the deoxygenated form the larger ferrous atom lies out of the plane of the porphyrin ring. (b) In the oxygenated form the now smaller “ferric-like” atom can slip into the plane of the porphyrin ring. As a result, the proximal histidine and the helix F into which it is incorporated are displaced. (Lehmann and Huntsman,61 with permission.)

In most of the hemoglobins M, tyrosine has been substituted for either the proximal or the distal histidine. Tyrosine can form an iron-phenolate complex that resists reduction to the divalent state by the normal metabolic systems of the erythrocyte. Four hemoglobins M are a consequence of substitution of tyrosine for histidine in the proximal and distal sites of the a and b chains. As shown in Table 49-2, these four hemoglobins M have been designated by the geographic names Boston, Saskatoon, Iwate, and Hyde Park. Analogous His®Tyr substitutions in the a chain of fetal hemoglobin have also been documented and have been designated hemoglobins FM-Osaka62 and FM-Fort Ripley.63


Another hemoglobin M, Hb MMilwaukee, is formed by substitution of glutamic acid for valine in the sixty-seventh residue of the b chain rather than substitution of tyrosine for histidine. The glutamic acid side chain points toward the heme group, and its g-carboxyl group interacts with the iron atom, stabilizing it in the ferric state.
It is rare for methemoglobinemia to occur as result of hemoglobinopathies other than hemoglobin M, but hemoglobinChile (b28 Leu®Met) is such a hemoglobin. Producing hemolysis only with drug administration, this unstable hemoglobin is characterized clinically by chronic methemoglobinemia.70
In some hemoglobin variants the deoxy conformation of the hemoglobin molecule is favored because the angle of the heme is altered from that found normally in deoxyhemoglobin. Such changes occur in HbHammersmith, HbBucuresti, HbTorino, and HbPeterborough. In other instances the quaternary conformation is changed by mutations involving the a1b2 contact (HbKansas, HbTitusville, and HbYoshizuka). Properties of abnormal hemoglobins associated with low oxygen affinity are summarized in Table 49-3.


In response to the improved tissue oxygen supply brought about by a right-shifted oxygen dissociation curve, the “oxygen sensor”73 of the body decreases the output of erythropoietin.71 As a result, the steady state level of hemoglobin is diminished; mild anemia is characteristic of patients with hemoglobins with a decreased oxygen affinity.
Sulfhemoglobin derives its name from the fact that it can be produced in vitro from the action of hydrogen sulfide on hemoglobin74 and that the feeding of elemental sulfur to dogs has been associated with sulfhemoglobinemia.75 Sulfhemoglobin may contain one excess sulfur atom.76,77 and 78 Sulfhemoglobinemia has been associated with the ingestionof various drugs, particularly sulfonamides, phenacetin, acetanilid, and phenazopyridine.79,80 It also occurs independent of drug use and has been thought to be related to chronic constipation or to purging.81 Some patients with sulfhemoglobinemia or a past history of this disorder appear to have increased levels of red blood cell GSH.82 The reason for this increase and its relationship to sulfhemoglobinemia is not clearly understood, but it may be of significance that some of the types of drugs which have been associated with sulfhemoglobinemia cause an elevation of red cell GSH levels,83 probably by activating the enzyme glutathione synthetase83 or by increasing intracellular glutamate levels.84
Cyanosis due to abnormal hemoglobins is inherited as an autosomal dominant disorder. In contrast, hereditary methemoglobinemia due to NADH-diaphorase deficiency is inherited in an autosomal recessive fashion. Evidence for the occurrence of hereditary sulfhemoglobinemia85 is not convincing, and it is likely that the single family reported represents a hemoglobin M hemoglobinopathy.
Methemoglobinemia may be chronic or acute. Severe acute methemoglobinemia, usually the consequence of drug ingestion or toxic exposure, can produce symptoms of anemia, since methemoglobin lacks the capacity to transport oxygen. Acutely developing levels of methemoglobin exceeding 60 to 70 percent of the total pigment may be associated with vascular collapse, coma, and death,24,29 although recovery was documented in one patient with a level as high as 81.5% of the total pigment.86
Chronic methemoglobinemia, whether due to exposure to drugs or toxins or to hereditary causes, is usually asymptomatic. In instances when the methemoglobin levels are very high (>20% of the total pigment) mild erythrocytosis is occasionally noted. Patients with hemoglobins M or with low oxygen affinity hemoglobin also manifest cyanosis. In the case of a-chain variants, the dusky color of the infants will be noted at birth, but the clinical manifestations of b-chain variants become apparent only after b-chains have largely replaced the fetal a-chains at 6 to 9 months of age. In spite of the impaired hemoglobin function, no cardiopulmonary symptoms are observed and there is no clubbing. In the case of Hb MSaskatoon and Hb MHyde Park hemolytic anemia with jaundice may be present. The hemolytic state may be exacerbated by administration of sulfonamides.87
Toxic Methemoglobinemia
In toxic methemoglobinemia an elevated level of methemoglobin is found, but the activity of NADH diaphorase is normal.
In hereditary methemoglobinemia due to NADH-diaphorase deficiency, between 8 and 40 percent of the hemoglobin is in the oxidized (methemoglobin) form. The blood may have a chocolate-brown color. NADH-diaphorase activity is best measured using ferricyanide as a receptor, measuring the rate of oxidation of NADH.88,89 The residual level of enzyme activity is usually less than 20 percent of normal in patients with methemoglobinemia due to deficiency of this enzyme. An immunoassay has been described,90 but such an assay would not detect mutants in which enzyme molecules with impaired catalytic activity are present. For unknown reasons, glutathione reductase activity is usually also diminished.91 Cytochrome b5 assays92 may be useful if diaphorase activity is normal.
The spectrum of normal methemoglobin A at pH 7.0 is illustrated in Fig. 49-2.93 Hemoglobins M may be differentiated from methemoglobin formed from hemoglobin A by their absorption spectra in the range of 450 to 750 nm. Since only some 20 to 35 percent of the total hemoglobin will ordinarily be hemoglobin M, the mixed spectra of methemoglobin A and hemoglobin M may be difficult to interpret. Therefore, it is preferable to perform these spectral studies on purified hemoglobin M isolated by electrophoretic or chromatographic means.61

FIGURE 49-2 Absorption spectra at pH 7.0. A; B, methemoglobin A; B, methemoglobin MBoston; C, methemoglobin MSaskatoon; D, methemoglobin A fluoride complex. For purposes of comparison all the optical densities have been made equal to 0.61 at 500 nm. (Gerald and George,93 with permission of the American Association for the Advancement of Science.)

All hemoglobin M samples should be converted to methemoglobin so that any difference found in electrophoresis will be due to the amino acid substitution and not to the different charge of the iron atom. Electrophoresis at pH 7.1 is most useful for separation of hemoglobins M since the imidazole groups of histidine have a net positive charge at this pH, while at higher pH levels the histidines and the substituting tyrosines are both neutral.
The hemoglobins M differ in their reactivity to cyanide and to azide ions.94
Sulfhemoglobin is detected in the lysate of blood treated with ferricyanide, cyanide, and ammonia by comparing the optical density at 620 nm with that at 540 nm.95,96
Cyanosis due to methemoglobinemia or sulfhemoglobinemia should be differentiated from cyanosis due to cardiac or pulmonary disease particularly when right-to-left shunting is present. In the latter instances the arterial oxygen tension will be low, while in methemoglobinemia and sulfhemoglobinemia it should be normal. One should be certain, however, that the oxygen tension was measured directly and not deduced from the percent saturation of hemoglobin. Blood from a patient with cyanosis due to arterial oxygen desaturation promptly becomes bright red upon being shaken with air. In addition, these causes of cyanosis are readily differentiated by carrying out quantitative blood methemoglobin and sulfhemoglobin levels. Because of the potential lethal nature of high levels of methemoglobin, and because prompt treatment may be life saving, a high index of suspicion is important. A patient with cyanosis whose arterial blood is brown with a that is found to be normal on blood gas examination is likely to have methemoglobinemia. One should not rely on the readings of a pulse oximeter, since false readings may be obtained in the presence of methemoglobin. Rapid examination of a blood sample using an automatic analyzer such as a CoOximeter is the first step in confirming the diagnosis. However, as pointed out under “Laboratory Features” above, although treatment should not be delayed, direct spectrophotometric analysis should be carried out on the pretreatment sample as soon as possible to distinguish between methemoglobinemia and sulfhemoglobinemia.
A family history is usually helpful in differentiating hereditary methemoglobinemia due to NADH-diaphorase deficiency from hemoglobin M disease. The former has a recessive mode of inheritance, the latter a dominant mode. Thus, cyanosis in successive generations suggests the presence of hemoglobin M; normal parents but possibly affected sibs implies the presence of NADH-diaphorase deficiency. Consanguinity is more common in NADH-diaphorase deficiency. In NADH-diaphorase deficiency incubation of the blood with small amounts of methylene blue will result in rapid reduction of the methemoglobin; in hemoglobin M disease such reduction does not take place. The absorption spectra of methemoglobin and its derivatives are normal in NADH-diaphorase deficiency; they are abnormal in hemoglobin M disease. In the case of toxic methemoglobinemia cyanosis is generally of relatively recent origin, and a history of exposure to drug or toxin may usually be obtained; in hereditary methemoglobinemia a history of lifelong cyanosis may usually be elicited.
Toxic Methemoglobinemia
Acute toxic methemoglobinemia may represent a serious medical emergency. Because of the loss of oxygen-carrying capacity of the blood and because of the left shift in the oxygen dissociation curve that occurs when methemoglobin is present in high concentration,97 acute methemoglobinemia may be life threatening when the level of the pigment exceeds half of the total circulating hemoglobin.
Methylene blue is an effective treatment for patients with methemoglobinemia because NADPH formed in the hexose monophosphate pathway can rapidly reduce this dye to leukomethylene blue in a reaction catalyzed by NADPH diaphorase. Leukomethylene blue, in turn, nonenzymatically reduces methemoglobin to hemoglobin.98 An exception to the efficacy of this treatment exists in those patients who are G-6-PD deficient (see Chap. 45). In these subjects methylene blue would not only fail to give the desired effect on methemoglobin levels but might compound the patient’s difficulty by inducing an acute hemolytic episode.99 In patients with acute toxic methemoglobinemia who are symptomatic or whose methemoglobin level is rising rapidly, the intravenous administration of 1 or 2 mg methylene blue per kg body weight over a period of 5 min is the preferred treatment because of its very rapid action.20 Use of excessive amounts of methylene blue should be avoided: the administration of repeated doses of 2 mg methylene blue/kg body weight has produced acute hemolysis even in patients with normal G-6-PD levels.21 The response to treatment is so rapid, with marked lowering or normalization of methemoglobin levels within an hour or two, that no other treatment is usually needed, but the patient should be observed carefully because continued absorption of a toxic substance from the gastrointestinal tract may cause recurrence of the methemoglobinemia. In patients who are in shock blood transfusion may be helpful. Cimetidine, used as a selective inhibitor of N-hydroxylation, may decrease the methemoglobinemia produced by dapsone in patients with dermatitis herpetiformis.100
The course of hereditary methemoglobinemia is benign, but patients with this disorder should be shielded from exposure to aniline derivatives, nitrites, and other agents which may, even in normal persons, induce methemoglobinemia. Hereditary methemoglobinemia due to NADH-diaphorase deficiency is readily treated by the administration of ascorbic acid, 300 to 600 mg orally daily divided into three or four doses. While intravenously administered methylene blue is very effective in correcting this type of methemoglobinemia, it is not suitable for the long-term therapy that needs to be given if the state is to be treated at all.
The iron phenolate complex which exists in the hemoglobins M prevents the reduction of ferric to ferrous iron. For these reasons the methemoglobinemia does not respond to administration of ascorbic acid or of methylene blue. No effective treatment exists for the cyanosis that is present in patients with abnormal hemoglobins with reduced oxygen affinity.
Sulfhemoglobinemia is almost always a benign disorder. Unlike methemoglobin, sulfhemoglobin does not produce a left shift in the oxygen dissociation curve but rather decreases the affinity of hemoglobin for oxygen.79 The disorder tends to recur repeatedly in the same persons after exposure to drugs but does not generally appear to affect their overall health. Unlike methemoglobin, sulfhemoglobin cannot be converted to hemoglobin. Thus, once sulfhemoglobinemia occurs it will persist until the erythrocytes carrying the abnormal pigment reach the end of their life span.

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Manabe J, Arya R, Sumimoto H, et al: Two novel mutations in the reduced nicotinamide adenine dinucleotide (NADH) cytochrome b5 reductase gene of a patient with generalized type, hereditary methemoglobinemia. Blood 88:3208, 1996.

Shirabe K, Fujimoto Y, Yubisui T, Takeshita M: An in-frame deletion of codon 298 of the NADH-cytochrome b5 reductase gene results in hereditary methemoglobinemia type II (generalized type). A functional implication for the role of the COOH-terminal region of the enzyme. J Biol Chem 269:5952, 1994.

Vieira LM, Kaplan J-C, Kahn A, Leroux A: Four new mutations in the NADH-cytochrome b5 reductase gene from patients with recessive congenital methemoglobinemia type II. Blood 85:2254, 1995.

Jenkins MM, Prchal JT: A novel mutation found in the 3′ domain of NADH-cytochrome B5 reductase in an African-American family with type I congenital methemoglobinemia. Blood 87:2993, 1996.

Shirabe K, Landi MT, Takeshita M, et al: A novel point mutation in a 3′ splice site of the NADH-cytochrome b5 reductase gene results in immunologically undetectable enzyme and impaired NADH-dependent ascorbate regeneration in cultured fibroblasts of a patient with type II hereditary methemoglobinemia. Am J Hum Genet 57:302, 1995.

Higasa K, Manabe J, Yubisui T, et al: Molecular basis of hereditary methaemoglobinaemia, types I and II: two novel mutations in the NADH-cytochrome b5 reductase gene. Br J Haematol 103:922, 1998.

Tanishima K, Tomoda A, Yoneyama Y, Ohkuwa H: Three types of hereditary methemoglobinemia due to NADH-cytochrome b5 reductase deficiency. Adv Clin Enzymol 5:81, 1987.

Takeshita M, Tamura M, Kugi M, et al: Decrease of palmitoyl-CoA elongation in platelets and leukocytes in the patient of hereditary methemoglobinemia associated with mental retardation. Biochem Biophys Res Commun 148:384, 1987.

Tanishima K, Tanimoto K, Tomoda A, et al: Hereditary methemoglobinemia due to cytochrome b5 reductase deficiency in blood cells without associated neurologic and mental disorders. Blood 66:1288, 1985.

Lo SC-L, Agar NS: NADH-methemoglobin reductase activity in the erythrocytes of newborn and adult mammals. Experientia 42:1264, 1986.

Graubarth J, Bloom CJ, Coleman FC, Solomon HN: Dye poisoning in the nursery: a review of seventeen cases. JAMA 128:1155, 1945.

Lukens JN: The legacy of well-water methemoglobinemia. JAMA 257:2793, 1987.

Hanukoglu A, Danon PN: Endogenous methemoglobinemia associated with diarrheal disease in infancy. J Pediatr Gastroenterol Nutr 23:1, 1996.

Cohen RJ, Sachs JR, Wicker DJ, Conrad ME: Methemoglobinemia provoked by malarial chemoprophylaxis in Vietnam. N Engl J Med 279:1127, 1968.

Hegesh E, Hegesh J, Kaftory A: Congenital methemoglobinemia with a deficiency of cytochrome b5. N Engl J Med 314:757, 1986.

Mansouri A, McClellan JL: Congenital methemoglobinemia with cytochrome b5 deficiency. N Engl J Med 315:893, 1986.

Tauber AI, Blanchard RA: Congenital methemoglobinemia with cytochrome b5 deficiency. N Engl J Med 315:894, 1986.

Lehmann H, Huntsman RG: Man’s Haemoglobins, p 213. Lippincott, Philadelphia, 1974.

Hayashi A, Fujita T, Fujimura M, Titani K: A new abnormal fetal hemoglobin, Hb FM-Osaka (a2g263His ® Tyr). Hemoglobin 4:447, 1980.

Priest JR, Watterson J, Jones RT, Faassen AE, Hedlund BE: Mutant fetal hemoglobin causing cyanosis in a newborn. Pediatrics 83:734, 1989.

Gerald PS, Efron ML: Chemical studies of several varieties of Hb M. Proc Natl Acad Sci USA 47:1758, 1961.

Staven P, Strome J, Lorkin PA, Lehmann H: Haemoglobin M Saskatoon with slight constant haemolysis, markedly increased by sulphonamides. Scand J Haematol 9:566, 1972.

Hayashi N, Motokawa Y, Kikuchi G: Studies on relationships between structure and function of hemoglobin M Iwate. J Biol Chem 241:79, 1966.

Hutt PJ, Pisciotta AV, Fairbanks VF, Thibodeau SN, Green MM: DNA sequence analysis proves Hb M-Milwaukee-2 is due to beta-globin gene codon 92 (CAC®TAC), the presumed mutation of Hb M-Hyde Park and Hb M-Akita. Hemoglobin 22:1, 1998.

Horst J, Schafer R, Kleihauer E, Kohne E: Analysis of the Hb M Milwaukee mutation at the DNA level. Br J Haematol 54:643, 1983.

Hain RD, Chitayat D, Cooper R, et al: Hb FM-Fort Ripley: confirmation of autosomal dominant inheritance and diagnosis by PCR and direct nucleotide sequencing. Hum Mutat 3:239, 1994.

Hojas-Bernal R, McNab-Martin P, Fairbanks VF, et al: Hemoglobin Chile beta 28(B10)Leu®met: an unstable hemoglobin associated with chronic methemoglobinemia and sulfonamide or methylene blue-induced hemolytic anemia. Hemoglobin 23:125, 1999.

Stamatoyannopoulos G, Parer JT, Finch CA: Physiologic implication of a hemoglobin with decreased oxygen affinity (hemoglobin Seattle). N Engl J Med 281:915, 1969.

Reissmann KR, Ruth WE, Namura T: A human hemoglobin with lowered oxygen affinity and impaired heme-heme interactions. J Clin Invest 40:1826, 1971.

Beutler E: “A shift to the left” or “a shift to the right” in the regulation of erythropoiesis. Blood 33:496, 1969.

Lemberg R, Legge JW: Hematin Compounds and Bile Pigments, Interscience Publishers, New York, 1949.

Harrop GA, Jr., Waterfield RL: Sulphemoglobinemia. JAMA 95:647, 1930.

Nichol AW, Hendry I, Morell DB: Mechanism of formation of sulphhaemoglobin. Biochim Biophys Acta 156:97, 1968.

Berzofsky JA, Peisach J, Horecker BL: Sulfheme proteins. IV. The stoichiometry of sulfur incorporation and the isolation of sulfhemin, the prosthetic group of sulfmyoglobin. J Biol Chem 247:3783, 1972.

Berzofsky JA, Peisach J, Blumberg WE: Sulfheme proteins. II. The reversible oxygenation of ferrous sulfmyoglobin. J Biol Chem 246:7366, 1971.

Park CM, Nagel RL: Sulfhemoglobinemia. Clinical and molecular aspects. N Engl J Med 310:1579, 1984.

Halvorsen SM, Dull WL: Phenazopyridine-induced sulfhemoglobinemia: inadvertent rechallenge. Am J Med 91:315, 1991.

Discombe G: Sulphaemoglobinaemia and glutathione. Lancet 2:371, 1960.

McCutcheon AD, Melb MD, Flack EH: Sulphaemoglobinaemia and glutathione. Lancet 2:240, 1960.

Paniker NV, Beutler E: The effect of methylene blue and diaminodiphenylsulfone on red cell reduced glutathione synthesis. J Lab Clin Med 80:481, 1972.

Smith JE, Mahaffey E, Lee M: Effect of methylene blue on glutamate and reduced glutathione of rabbit erythrocytes. Biochem J 168:587, 1977.

Miller AA: Congenital sulfhemoglobinemia. J Pediatr 51:233, 1957.

Caudill L, Walbridge J, Kuhn G: Methemoglobinemia as a cause of coma. Ann Emerg Med 19:677, 1990.

Dacie JV, Lewis SM: Chemical and physico-chemical methods of haematological importance, in Practical Haematology. pp 476–524. Grune and Stratton, New York, 1998.

Beutler E: Red Cell Metabolism: A Manual of Biochemical Methods. Grune and Stratton, New York, 1984.

Board PG: NADH-ferricyanide reductase, a convenient approach to the evaluation of NADH-methaemoglobin reductase in human erythrocytes. Clin Chim Acta 109:233, 1981.

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Gerald PS, George P: A second spectroscopically abnormal methemoglobin associated with hereditary cyanosis. Science 129:393, 1959.

Carrell RW, Kay R: A simple method for the detection of unstable haemoglobins. Br J Haematol 23:615, 1972.

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Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology



Definition and History
Etiology and Pathogenesis

Mode of Inheritance
Clinical Features
Laboratory Features
Differential Diagnosis
Treatment, Course, and Prognosis
Chapter References

Mutations that cause destabilization of the hemoglobin tetramer are an uncommon cause of hemolytic anemia. In contrast to the hemolytic anemias caused by enzyme deficiencies, a dominant mode of inheritance characterizes the unstable hemoglobins. Heinz bodies are a characteristic feature of the red cells in the blood when splenectomy has been carried out. Hemolytic anemia may be precipitated by the ingestion of oxidative drugs. The diagnosis is established by precipitating the unstable hemoglobin in a system in which the hemolysate is heated or incubated in a mixture of isopropanol and buffer. Although splenectomy has occasionally ameliorated the anemia, it should be avoided in most cases, because it has sometimes been followed by fatal thromboembolic complications.

The sporadic occurrence of hemolytic anemia with the appearance of inclusion bodies in the red cells was occasionally observed in the 1940s and 1950s,1,2 and 3 but it was not until 19624,5 that it was recognized that such patients had abnormal hemoglobins that spontaneously denatured within the circulating red cell. The unstable hemoglobins that will be discussed in this chapter are those that result from a mutation that changes the amino acid sequence of one of the globin chains. Homotetramers of normal b chains (hemoglobin H) or normal g chains (hemoglobin Barts) are also unstable hemoglobins. These unstable hemoglobins occur in patients with a thalassemia and are discussed in Chap. 46. Hyperunstable hemoglobins6 have defects that are so severe that the globin chain is not found in the red cells, but their formation can be deduced from the DNA sequence.
The tetrameric hemoglobin molecule has evolved so that a variety of noncovalent forces maintain the structure of each subunit and bind the subunits to each other. The delicate balance that allows the molecule to change from one state to another, facilitating its oxygen-binding function while maintaining its structural integrity, has been discussed in Chap. 28. It is not surprising that a variety of amino acid substitutions or deletions will weaken the forces that maintain the structure of hemoglobin. When this occurs, the hemoglobin molecule denatures and precipitates as insoluble globins. These precipitates often attach to the cell membrane and are recognized as Heinz bodies.
Instability of hemoglobin can arise from any one of the following processes:

Replacement of an amino acid that contacts the heme group or produces a change in the property of the heme pocket often results in an unstable molecule with a tendency to lose heme from the abnormal globin chains. HbHammersmith,7,8 HbSendagi, HbAlesha,10 and HbLa Roche-sur-Yon11 are examples of this type of unstable hemoglobin.

Replacement of nonpolar by polar residues at the interior of the molecule results in gross distortion of the protein, particularly if the new polar residue remains in the interior portion of the molecule, as in HbBristol12 and HbVolga.13

Deletions or insertions of additional amino acids, particularly when critical helical regions of the sequence are involved, creates instability, as in HbNiteroi14 and HbMontreal.15

Replacements at intersubunit contacts, particularly those between the a1 and b1 chain, create instability so that dissociation into monomers may occur. HbPhilly16 and HbTacoma17 are mildly unstable for this reason. Replacements at the contact between the a1 and b2 globin monomers usually result in hemoglobins with a high oxygen affinity.

If proline is introduced into an a helix beyond the third residue, distortion of the helix results in instability.18 Variants in which proline substitution results in instability include HbDuarte19 and HbSanta Ana.20

In areas of the hemoglobin molecule in which atoms are very tightly packed, substitution of amino acids with larger side chains for glycine may produce marked changes in stability. In particular, at the points where the B and E helices approach each other there is no room for the substitution of larger amino acids for glycine at B6 and E8. HbRiverdale-Bronx,21 HbSavannah,22 and HbMoscva23 arise in such a fashion.

Replacement of a hydrophobic residue that normally fits into a hydrophobic pocket with a more hydrophilic amino acid, such as the substitution of histidine for leucine at b81 in HbLa Roche-sur-Yon.11
Many unstable hemoglobins have an increased susceptibility to oxidation to methemoglobin. However, the exact sequence of events that leads to the precipitation of hemoglobin is not fully understood and very likely varies with different unstable hemoglobins. The formation of hemichromes may be involved. These are compounds in which heme has been removed from its normal binding site and has become bonded to another part of the globin molecule.24 These pigments can be shown to form during in vitro denaturation of some abnormal hemoglobins,25 and they are present in hemoglobin H inclusion bodies.26 The release of activated oxygen in the form of superoxide radicals with the subsequent formation of peroxide and the hydroxyl radicals27,28 may also play a role. The attachment of Heinz bodies to the cell membrane impairs the deformability of the erythrocyte and impedes its ability to negotiate the narrow spaces between the endothelial cells lining the splenic sinuses. The “pitting” of Heinz bodies from the erythrocyte results in loss of membrane and ultimately in destruction of the red cells. Although Heinz bodies are formed, their presence in the blood does not become a prominent feature except in patients who have been splenectomized (see “Laboratory Features”). Selected unstable hemoglobins that have been characterized are listed in Table 48-1. Detailed tabulations are available.29


Hyperunstable hemoglobins are characterized by b-globin formation that is so defective that no b-chains are found. However, they differ from the b-thalassemias in that inheritance is dominant, i.e., a single copy of the mutant gene is all that is required to give the clinical phenotype. They may be due to single base substitution, deletion of codons, frameshifts leading to elonged b-chains, or premature terminations.30
Unstable hemoglobins are generally inherited as autosomal dominant disorders. Affected individuals are usually heterozygotes who have inherited the defect from one of their parents and who on the average will transmit it to one-half of their offspring. Since unstable hemoglobins produce a disease state, genes for these disorders are subjected to negative selection, and the continued existence of the unstable hemoglobinopathies in the population is the result of such new mutations. Thus, occasionally patients with an unstable hemoglobin are encountered neither of whose parents had the abnormality. The homozygous state for the unstable hemoglobins HbSun Prairie31 and HbBushwick32 have been observed, and a homozygous-like state can occur when an unstable b chain mutation is inherited together with a bo thalassemic gene.19,33
Over 80 percent of unstable hemoglobins that have been characterized affect the b chain. This probably reflects the fact that the normal genome contains four copies of the a chain. The clinical effects of such mutants, affecting only one-fourth of the total hemoglobin formed, is apt to be less pronounced than those of b-chain mutants, in which one-half of the hemoglobin produced is abnormal. Thus, many a-globin mutations are likely to be overlooked.
Although most patients with unstable hemoglobins have been found to have a combination of hemoglobin A and the unstable hemoglobin in their red cells, there are a number of reports of the inheritance of unstable hemoglobins with other hemoglobinopathies.19,34,35,36,37 and 38
A broad spectrum of clinical manifestations can be induced by unstable hemoglobins. In most cases, hemolysis is well compensated, and some hemoglobins that are unstable in vitro (e.g., HbMuscat39) are not associated with hemolysis at all. When an unstable hemoglobin also has a left-shifted oxygen dissociation curve, i.e., a raised O2 affinity, the hemoglobin level may be in the upper portion of the normal range. Episodes of infection and treatment with “oxidant” drugs are likely to precipitate hemolytic episodes in persons whose anemia is well compensated under ordinary circumstances. It is at this juncture that the diagnosis is often first made. In the case of patients who have particularly unstable variants, such as HbHammersmith,7 HbBristol,12 HbSanta Ana,20 or HbMadrid,40 a chronic hemolytic anemia may become evident during the first year of life as g chain production is replaced by production of the mutant b chain. In contrast, in the rare instances where the g chain bears the abnormality,41 the hemolytic anemia is evident at birth, and it disappears as normal b chains are formed.
Physical findings include jaundice, splenomegaly, and, when the anemia is severe, pallor. In some patients, dark urine has been observed, probably as a result of the excretion of dipyrrole pigments derived from the catabolism of free heme groups or of Heinz bodies.42 In some instances methemoglobulinemia may develop, and cyanosis may then be evident.
The hemoglobin concentration of the blood may be normal or decreased. The mean corpuscular hemoglobin is usually diminished because of the loss of hemoglobin from the red cells as a result of its denaturation and subsequent pitting from the erythrocytes. The blood film may show slight hypochromia, and, in addition, poikilocytosis, polychromasia, anisocytosis, and some basophilic stippling may be evident. Hyperunstable hemoglobins, in particular, are associated with severe hypochromia of the erythrocytes and present clinically as dominant b-thalassemia. Reticulocytosis is often out of proportion to the severity of the anemia, particularly when the abnormal hemoglobin has a high oxygen affinity. After splenectomy many Heinz bodies may be found in the circulation. Hemoglobin F levels may be increased.43
Diagnosis of this disorder usually depends upon the demonstration of the presence of an unstable hemoglobin. Three tests are used for this purpose. The most convenient is the isopropanol stability test.44 The heat stability test is also useful45 but is somewhat more difficult to interpret. It has been found, however, that at least one unstable hemoglobin, hemoglobin Olmsted, can be detected by heat stability but not isopropanol stability.46 Finally, incubation of blood with brilliant cresyl blue generates Heinz bodies in hemoglobin H disease.47,48 Further identification of unstable hemoglobins is aided by procedures such as hemoglobin electrophoresis; however, the electrophoretic pattern is often normal, and the diagnosis of the hemoglobinopathy cannot be ruled out in this way. The oxygen affinity of unstable hemoglobins is often altered, and the determination of the P50 may help in detecting and characterizing the unstable hemoglobin. In the final analysis unstable hemoglobins can be identified only by DNA analysis10,43,49,50 or by physical separation of the abnormal hemoglobin from the normal hemoglobin, followed by globin chain separation and peptide analysis.
The possibility that an unstable hemoglobin is present should be considered in all patients who present with the clinical picture of hereditary nonspherocytic hemolytic anemia (Chap. 45), particularly when hypochromia of the red cells is present and when the extent of the reticulocytosis is out of keeping with the degree of anemia. Not all patients with a positive test for unstable hemoglobins should be classified as having this disorder. The stability of methemoglobin, hemoglobin F, and sickle hemoglobin is appreciably less than that of hemoglobin A, and false-positive isopropanol stability tests may be obtained in patients with increased quantities of these hemoglobins. Hemoglobin H (b4) and hemoglobin Barts (g4) are unstable. These fast-moving hemoglobins can be detected on electrophoresis. Patients whose red cells contain these hemoglobins are diagnosed as having a thalassemia (see Chap. 46).
Sometimes the hemoglobins are so unstable that none of the protein can be detected. Such abnormal hemoglobins have been diagnosed by DNA-based analysis.10,43,49,50
Most patients with unstable hemoglobins follow a relatively benign course. As with other hemolytic states, gallstones are common, and cholecystectomy may be required. Hemolytic episodes may be precipitated by infection or by the ingestion of “oxidative” drugs. Sulfonamides have been particularly prominent in inducing hemolysis, and derivatives that do not produce hemolysis in G-6-PD deficiency have been shown to precipitate hemolysis in patients with some unstable hemoglobins. A few deaths that are believed to have been directly related to unstable hemoglobins have been reported. A patient with HbHirosaki is thought to have died following a hemolytic crisis precipitated by a common cold.51 Two sisters with HbDuarte19 died of thromboembolic complications less than a year following splenectomy. This unstable variant has an increased oxygen affinity, and it is likely that a combination of postsplenectomy erythrocytosis and thrombocytosis led to the demise of the patients.
Treatment is not usually required. As in the case of other hemolytic disorders, folic acid in a dose of 1 mg per day is often given, but its usefulness has not been established. “Oxidant” drugs such as those listed in Table 45-5 should be avoided. In addition, the use of all sulfonamides should be eschewed, particularly in the case of those variants which have been associated with drug-induced hemolysis. Splenectomy has proved to be useful in some patients with splenomegaly and severe hemolysis,52,53 while others have enjoyed little benefit.46 In view of the fact that patients with high-oxygen-affinity unstable hemoglobin have died after a splenectomy19 and that thromboembolic complications have been reported in a number of other patients,54 it is probably best to avoid splenectomy. Preliminary results suggested that hydroxyurea therapy might be useful,53 presumably by increasing the level of fetal hemoglobin.

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Winterbourn CC, Carrell RW: Studies of hemoglobin denaturation and Heinz body formation in the unstable hemoglobins. J Clin Invest 54:678, 1974.

Girodon E, Ghanem N, Vidaud M, et al: Rapid molecular characterization of mutations leading to unstable hemoglobin b-chain variants. Ann Hematol 65:188, 1992.

Landin B, Astrom M: Unstable haemoglobin causing haemolytic anaemia: de novo mutation in Sweden identified by PCR. J Intern Med 233:299, 1993.

Ohba Y, Miyaji T, Matsuoka M, et al: Hemoglobin Hirosaki (alpha 43 (CD1) Phe®Leu): a new unstable variant. Biochim Biophys Acta 405:155, 1975.

Vichinsky EP, Lubin BH: Unstable hemoglobins, hemoglobins with altered oxygen affinity, and M-hemoglobins. Pediatr Clin North Am 27:421, 1980.

Rose C, Bauters F, Galacteros F: Hydroxyurea therapy in highly unstable hemoglobin carriers. Blood 88:2807, 1996.

Thuret I, Bardakdjian J, Badens C, et al: Priapism following splenectomy in an unstable hemoglobin: Hemoglobin Olmsted beta141 (H19) Leu®Arg. Am J Hematol 51:133, 1996.
Copyright © 2001 McGraw-Hill
Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology



Williams Hematology



Definition and History
The Sickle Cell Diseases

Etiology and Pathogenesis

Clinical Features

Laboratory Features


Therapy, Course, and Prognosis

Sickle Cell Trait

Definition and History

Etiology and Pathogenesis

Clinical Features

Laboratory Features

Therapy, Course, and Prognosis
Hemoglobin C Disease

Definition and History

Etiology and Pathogenesis

Clinical Features

Laboratory Features

Differential Diagnosis

Therapy, Course, and Prognosis
Hemoglobin D Disease

Definition and History

Etiology and Pathogenesis

Clinical Features
Hemoglobin E Disease

Definition and History

Etiology and Pathogenesis

Clinical Features

Laboratory Features

Therapy, Course, and Prognosis
Other Hemoglobinopathies
Chapter References

Sickle hemoglobin is a mutant hemoglobin in which valine has been substituted for the glutamic acid normally at the sixth amino acid of the b-globin chain. This hemoglobin polymerizes and becomes poorly soluble when the oxygen tension is lowered, and red cells that contain this hemoglobin become distorted and rigid. Sickle cell disease occurs when an individual is homozygous for the sickle cell mutation or is a compound heterozygote for sickle hemoglobin and b-thalassemia, hemoglobin C, or some less common b-globin mutations. Diagnosis depends upon demonstrating the presence of the abnormal hemoglobin(s) in the red cells. The disease is characterized by hemolytic anemia and by three types of crises: painful (vasoocclusive), sequestration, and aplastic. Complications include splenic infarction and autosplenectomy, stroke, bone infarcts and aseptic necrosis of the femoral head, leg ulcers, priapism, pulmonary hypertension, and renal failure. The severity of clinical manifestations varies greatly from patient to patient and the aggressiveness of treatment needs to be modified accordingly. Early diagnosis, immunization against pneumococcal infection, and prompt treatment of infections that do occur has contributed to greatly improved survival of those born with these disorders. Stem cell transplantation, when successful, cures the disease. Treatment with hydroxyurea increases the fetal hemoglobin level and can result in amelioration of crises. Sickle trait, the heterozygous state for sickle hemoglobin, affects some eight percent of African Americans, and with rare exception is entirely benign. Hemoglobin C disease is associated with splenomegaly but minimal hematologic changes, and the rare hemoglobin D disease is essentially asymptomatic. Hemoglobin E is very common in some parts of Asia. This hemoglobin is greatly underproduced, and the homozygous state or compound heterozygous state with b-thalassemia resembles thalassemia.

Acronyms and abbreviations that appear in this chapter include: BPG, bisphosphoglycerate; G-6-PD, glucose-6-phosphate dehydrogenase; MCHC, mean corpuscular hemoglobin concentration; VLA-4, very late activation antigen-4.

James Herrick, the astute Chicago physician who is also credited with description of the clinical syndrome of coronary thrombosis, was the first to observe sickled cells in the blood of an anemic African graduate student1 (Fig. 47-1). Emmel2 demonstrated that red cells sickled when blood from such patients was sealed under glass and allowed to stand at room temperature for several days, but the fact that the transformation to sickled cells occurs in response to a fall in oxygen tension was not recognized until the classic studies of Hahn and Gillespie in 1927.3 In 1923 the sickling phenomenon was shown to be inherited as an autosomal dominant trait.4 Much later, Neel5 and Beet6 clarified the genetic basis of sickle cell anemia by demonstrating that heterozygosity for the sickle cell gene resulted in sickle cell trait without significant clinical symptoms, while homozygosity resulted in sickle cell anemia.

FIGURE 47-1 Peculiar elongated and sickle-shaped red corpuscles in a case of severe anemia. (Herrick,1 by permission.)

In 1949 Pauling and his colleagues7 found that all the hemoglobin in patients with sickle cell anemia showed an abnormally slow rate of migration on electrophoresis, while the parents of the these patients had normal as well as abnormal hemoglobin. Soon after, other abnormal hemoglobins were discovered by subjecting hemoglobin to electrophoresis. The biochemical nature of the defect in sickle cell anemia was elucidated by Ingram,8 who digested hemoglobin with trypsin and separated the resulting peptides on paper by electrophoresis in one direction and chromatography in the other. This technique (“fingerprinting”) demonstrated that one of the digestion products of sickle hemoglobin migrated differently from that of normal hemoglobin. Determination of the amino acid composition of this peptide indicated that sickle cell anemia was the result of the replacement of a glutamic acid residue by valine. This discovery established that the substitution of a single amino acid in a polypeptide chain can alter the function of the gene product sufficiently to produce widespread clinical effects. Conley has chronicled the fascinating history of sickle cell disease.9
After the discovery that sickle hemoglobin, or hemoglobin S (Hb S), was electrophoretically altered, additional variants were assigned letters of the alphabet—C, D, E, etc. The letters of the alphabet were rapidly exhausted, however, and subsequent abnormal hemoglobins were named after the geographic location in which they were found (e.g., hemoglobin Memphis, hemoglobin Mexico). If the hemoglobin had the electrophoretic characteristics of one previously described by a letter, the geographic designation was added as a subscript (e.g., hemoglobin MSaskatoon). In this case M indicates an amino acid substitution resulting in a methemoglobin. In a fully characterized hemoglobin the amino acid substitution is designated by a superscript to the globin chain involved, as, for example, hemoglobin S, a2b26 Glu®Val and hemoglobin GNorfolk, a235 Asp®Asnb2. Thus, this notation indicates that hemoglobin S has a substitution of valine for glutamic acid in the sixth position of the b chain and that hemoglobin GNorfolk is a substitution of asparagine for aspartic acid in the thirty-fifth position of the a chain.
The term sickle cell disorder refers to states in which the red cell undergoes sickling when it is deoxygenated. The sickle cell diseases are those disorders in which sickling produces prominent clinical manifestations. Included are sickle cell–hemoglobin C disease (hemoglobin SC disease), sickle cell–hemoglobin D disease (hemoglobin SD disease), sickle cell b-thalassemia, and sickle cell anemia. The latter term is reserved for the homozygous state for the sickle cell gene.
Sickle cell anemia (SS disease) may be considered the prototype of the sickle cell diseases, and in general the clinical features and treatment of all these disorders are the same and are therefore considered together here. The homozygous state, sickle cell anemia, is the most severe of these disorders, with hemoglobin SC disease and sickle cell b-thalassemia tending to be somewhat milder, and hemoglobin SD disease being the mildest of the group. However, there is a great deal of overlap in the severity of the clinical manifestations of these disorders, and they are therefore described together here. Some patients with sickle cell thalassemia or hemoglobin SC disease may be more anemic and have more severe and frequent crises than some mildly affected patients with sickle cell anemia. A major difference among these diseases is in their laboratory diagnosis.
There are few diseases of man whose etiology can be traced to as basic a level as sickle cell disease. Sickle cell anemia is due to the substitution of thymine for adenine in the glutamic acid DNA codon (GAG®GTG), which results, in turn, in substitution of b6 valine for glutamic acid. As discussed in Chap. 28, hemoglobin exists in two conformations, designated the oxy (relaxed, R) and deoxy (tense, T) states. Deoxygenation of hemoglobin shifts this equilibrium toward the T conformation. Molecules of deoxyhemoglobin S have a strong tendency to aggregate, and such aggregation requires the substitution of valine for glutamic acid in the b6 position, since only those hemoglobin variants with this substitution (e.g., S and Harlem) undergo sickling. Certain other structural features of the molecule are also of importance.10,11
Electron micrographs of deoxygenated sickle hemoglobin show the presence of multiple microtubules consisting of hemoglobin molecules stacked on top of each other (Fig. 47-2). The molecules do not lie directly over one another, so that a helical structure is formed. Fourteen strands of the fiber are organized into pairs,12 giving rise to a fiber that is 21 nm in diameter. Most of the intermolecular contacts that give rise to this structure have been elucidated.12,13

FIGURE 47-2 Electron micrograph of negatively stained fiber of hemoglobin S and the structure deduced by three-dimensional image reconstruction. The reconstructed fiber is presented as ball models, with each ball representing a hemoglobin S tetramer. The models are presented as the outer sheath (left), the inner core (center), and a combination of both inner and outer filaments (right). (Edelstein,452 by permission.)

The deoxygenated hemoglobin solution turns into a firm gel. The distorted sickled red cell is the visible end result of this molecular aggregation. The process is time dependent.14 Initially there is a rate-limiting nucleation process; a few molecules of sickle hemoglobin must aggregate, forming a “seed” on which aggregation of further molecules occurs rapidly. Thus, the sickling process is characterized by a long delay that is strongly dependent on temperature and concentration.15 The delay is inversely proportional to approximately the thirtieth power of the hemoglobin concentration.16 This delay is quite important in protecting the patient from even more dire consequences than might otherwise be anticipated. Even though the oxygen concentration of venous blood is sufficiently low so that at equilibrium about 85 percent of the red cells would contain sickle hemoglobin polymer, kinetic data suggest that about 80 percent of cells are prevented from sickling during their round trip through the circulation because they reach the lungs and become reoxygenated before significant polymerization has occurred.14
When a cell sickles and unsickles repeatedly, the membrane is affected and the cell becomes irreversibly sickled; it remains so even when the oxygen pressure is increased. These are the sickled forms seen on air-dried films. An irreversibly sickled cell has a high hemoglobin concentration and a high calcium and low potassium content, and it may be ATP-depleted.17 These cells appear to be derived directly from reticulocytes18 but have a short intravascular life span, and the severity of the hemolytic process is directly related to the number of these cells in a patient’s circulation.19 However, the relationship between the number of irreversibly sickled cells and the number and severity of painful crises is an inverse one.20,21
Although the primary defect in sickle cell disease is clearly in the hemoglobin, secondary alterations in red cell metabolism and membrane structure and function have also been described. Rapid potassium loss occurs early in the sickling process.22 Abnormalities of sickle cell membrane phosphorylation have been documented.23,24 and 25 The calcium pump is abnormal.26 Although the calcium content of sickle cell membranes, particularly of those cells that are irreversibly sickled, has been found to be increased,17,23,24,25,26 and 27 the location of the excess calcium appears to be in endocytic vacuoles, so that from a functional point of view its location is extracellular.28,29 Increased generation of free radicals may occur in sickle cells,30,31 and 32 and there is abnormal oxidation of thiols in sickle cells.33 Superoxide dismutase activity of sickle cells is slightly reduced,34 and the amount of NAD+ and the NAD++NADH/NADH ratio are increased.35 The binding of glyceraldehyde phosphate dehydrogenase to the membrane is decreased by 35 to 50 percent,36 and there appears to be uncoupling of the lipid bilayer from the submembrane skeleton.37 Macrophages seem to ingest sickle cells more readily than normal cells, and this could be a result of excessive auto-oxidation of membrane components with the acquisition of immunoglobulins on the cell surface38 or to loss of membrane phospholipid asymmetry, which is a constant finding in sickle cells39,40 and may play an important role in their clearance from the circulation as well as in activation of coagulation.
Because a large number of inherited and acquired factors influence the pathogenesis of clinical symptoms, the sickle cell disorders vary in clinical severity from the virtually symptomless sickle cell trait to the potentially lethal state characteristic of sickle cell anemia. Wide variation in the severity of clinical manifestations also occurs among patients with sickle cell anemia. Some die within the first few years of life, while others have been discovered late in life as a result of a chance survey.
Both intracellular and extracellular factors influence sickling. Included are the types of hemoglobin in the cell and their concentration, the level of 2,3-bisphosphoglycerate (2,3-diphosphoglycerate; 2,3-BPG; 2,3-DPG), and the hydrogen ion concentration. Some of these factors are determined predominantly by genetic factors; others are environmentally modified. The variability of these factors as well as many others that are not understood probably accounts for the natural pattern of this group of diseases—periods of comparative well-being interspersed with periods of clinical deterioration (crises). Longitudinal studies of patients have suggested that an increase in the number of dense and poorly deformable cells precedes the development of a crisis.41 However, calculation of the mean polymer fraction from the 2,3-BPG concentration, the MCHC, the internal pH, and the percent nonsickle hemoglobin did not make it possible to predict clinical course.42 The precipitating circumstances responsible for the development of crises are often not clear. Of those events that appear to be associated with the appearance of crises, infections are probably among the most common.
However, it is not only the extent of sickling that is important but also the interaction of the sickled cells with the endothelium and other blood cells (see “Blood Flow in the Microvasculature,” below).
Concentration of Hemoglobin S in the Red Cell A correlation exists between the concentration of sickle hemoglobin within a red cell and the susceptibility of the cell to sickling. The red cells of the sickle cell carrier, who is virtually symptom-free, always contain less than 50 percent Hb S; the remainder is largely normal adult hemoglobin. The exact proportions vary from one individual to another. It was proposed many years ago that the distribution of the concentration of sickle hemoglobin in the red cells of subjects with the sickle cell trait was bimodal.43 Subsequent studies confirmed the existence of more than a single mode and indicated that the distribution might actually be trimodal.44 The reason for such a discontinuous distribution has become apparent with the recognition of the very high frequency of a-thalassemia in persons of African ancestry. Individuals carrying a-thalassemic genes have a higher ratio of hemoglobin A to hemoglobin S than those who have four normal copies of the a locus.45 Apparently the affinity of a chains for bA chains is higher than its affinity for bS chains,46 possibly because of differences in the charge of the two chains.47 Thus, when the number of a chains becomes limiting in the formation of hemoglobin tetramers, a higher proportion of a2b2A tetramers than of a2b2S tetramers are formed. Interaction of the a-thalassemic gene and the sickle gene also may influence the course of sickle cell disease: the lower corpuscular hemoglobin concentration in the red cells in a-thalassemia would be expected to protect against sickling. It has been suggested that such an interaction may influence the severity of sickle cell disease in African Americans45,48,49 and that it may play an important role in producing the very mild clinical manifestation of sickle cell anemia in Saudi Arabia.50
The Presence of Other Hemoglobins in the Cell Other hemoglobins present in a red cell containing sickle hemoglobin are not inert bystanders in the sickling process.51 Some hemoglobins, such as F, Korle-Bu, and A2, interact less effectively with hemoglobin S than does hemoglobin A in the sickling process. Two common abnormal hemoglobins, Hb C and Hb D, and the relatively rare hemoglobin OArab become involved in the formation of the sickling tubule. The interaction of these hemoglobins with sickle hemoglobin increases the propensity of red cells to sickle. Moreover, the red cells of patients with SC disease characteristically have an increased MCHC, presumably due to a transport defect, and this too greatly increases sickling.52,53
Other hemoglobins do not appear to play an active role in the sickling process, and their presence in the red cell can greatly reduce the clinical severity of sickle cell anemia. Fetal hemoglobin, for example, protects the red cell from sickling.54 It is distributed heterogeneously in the red cells of an SS homozygote,55,56 and those cells with the largest amount are least susceptible to sickling.55,56 The relatively mild clinical manifestations of patients in the Middle East with sickle cell anemia has been ascribed at least in part to the high level of fetal hemoglobin present in their red cells.57,58 and 59 In the United States, however, no significant correlation exists between fetal hemoglobin levels and the severity of the clinical manifestations of sickle cell anemia,60 and even in the Arab population the relationship is not always clear,61 although it may be that the effect is obscured by a threshold phenomenon,62 i.e., that a favorable effect of fetal hemoglobin concentration is observed only above a certain level. In adults who are heterozygotes for hemoglobin S and hereditary persistence of hemoglobin F, hemoglobin S constitutes more than 70 percent of the hemoglobin, but the high concentration of hemoglobin F inhibits sickling because the distribution is such that each cell contains a considerable amount of hemoglobin F, and the patients experience a benign clinical course.63 The presence of the abnormal hemoglobin Memphis (a23Glu®Glnb2) also decreases the clinical severity of sickle cell disease,64 presumably by inhibiting the formation of the sickle tubule.
Interaction of Sickling and Thalassemia The interaction of b-thalassemia with sickling is discussed in Chap. 46, and that with a-thalassemia is considered above.
Glucose-6-Phosphate Dehydrogenase Deficiency It has been suggested that G-6-PD deficiency may have a beneficial effect on the clinical course of sickle cell anemia,65,66,67 and 68 but this correlation has not been confirmed in other studies.69,70,71,72,73,74,75 and 76 It has also been proposed that hemolytic crises are more common in patients with sickle cell disease who are also G-6-PD deficient.77 However, it seems unlikely that the G-6-PD-deficient cells of such a patient would be particularly sensitive in hemolytic stress; G-6-PD A– is very age labile (Chap. 45), and because the erythrocytes are young they have relatively normal G-6-PD activity. In Jamaica,74 the United States,75 and Brazil76 G-6-PD deficiency did not influence parameters of disease severity such as hemoglobin concentration, reticulocyte count, hemoglobin F concentration, irreversibly sickled cell counts, or plasma hemoglobin concentration, and there was no relationship between clinical severity and presence or absence of G-6-PD deficiency.
Pyruvate kinase deficiency is characterized by an increase of red cell 2,3-BPG levels (see Chap. 45). A patient with sickle trait who had inherited pyruvate kinase deficiency manifested sickling similar in severity to that in some patients with sickle disease.78
Deoxygenation Deoxygenation for a sufficient period of time is the most important factor determining the occurrence of sickling in a red cell containing hemoglobin S. The degree of deoxygenation required to produce sickling varies with the percentage of hemoglobin S in the cells. Red cells from patients with sickle cell anemia will begin to sickle at an oxygen tension of about 40 torr.79 Changes that impair adequate oxygenation of the blood may be deleterious to any person whose red cells contain sickle hemoglobin.
An arterial oxygen tension of about 66 torr is found at about 10,000 ft (3000 m). Hypoxemia may also result from flying in unpressurized aircraft; most commercial aircraft, however, maintain an atmospheric pressure in the cabin equivalent to that encountered at an altitude of 5000 to 7000 ft (1500 to 2100 m). Occasional patients with sickle cell anemia or hemoglobin SC disease have been reported to experience painful crises or splenic infarctions under such circumstances.80 However, there is no evidence that a person with sickle cell trait is at risk in a pressurized airplane.81 The oxygen content of the air may also be reduced during anesthesia or when an artificial breathing apparatus is used improperly, as in scuba diving. If pulmonary or cardiac function deteriorates (e.g., in pneumonia or in cardiac failure), any resulting reduction in arterial oxygen tension may prove hazardous to a patient with sickle cell disease.
Vascular Stasis The PO2 level producing in vitro sickling of cells containing Hb S bears only an indirect relationship to clinical measurements of arterial and venous PO2. This is because the PO2 in the larger peripheral vessels does not accurately reflect the oxygen tension in areas of vascular stasis, such as the sinusoids of the spleen, in which hypoxemia is common and sickling is likely to occur. Although a period of 2 to 4 min is required for the development of marked red cell distortion14,82 and rigidity, the red cells normally remain within the venous circulation for only about 10 to 15 s. For this reason, red cells in areas of vascular stasis are more vulnerable to sickling. Once sickling has occurred, increased blood viscosity83 results in further vascular stasis, further sickling, possible vascular occlusion, and infarction. This course of events leads to tissue death, manifested clinically as a painful crisis.
While no organ of the body is immune to vasoocclusion due to in vivo sickling, certain sites notorious for circulatory stasis are characteristically affected. Splenic and marrow infarctions due to vascular stasis are particularly frequent, and priapism may occur in the male. The role of vascular stasis in the development of leg ulcers and of retinal and renal lesions is discussed below under “Clinical Features.” Studies from Jamaica indicated that the incidence of peptic ulcer was greatly increased in patients with sickle cell disease,84 ulceration being identified in 30.5 percent of male patients over the age of 25, but this could not be confirmed in a West African population.85
Temperature Even though cold temperatures retard hemoglobin polymerization, low temperatures tend to precipitate sickle crises, presumably because of the accompanying vasoconstriction.
Acidosis Hydrogen ions produce a right shift in the oxygen dissociation curve (the Bohr effect), presumably by displacing the equilibrium between the high-affinity oxy conformation and the low-affinity deoxy conformation toward the deoxy conformation of hemoglobin. Since it is sickle hemoglobin in the deoxy conformation that aggregates, the lowered pH profoundly affects the sickling of red cells, even when the percent oxygenation is maintained at a constant level.86,87 Alkalosis, on the other hand, by shifting the equilibrium toward the oxy conformation, tends to retard sickling but impairs oxygen release to tissue.
Corpuscular Hemoglobin Concentration The tendency of hemoglobin S solutions to aggregate is proportional to the thirtieth power of the concentration.16,88 Accordingly, sickling of red cells is markedly influenced by the concentration of sickle hemoglobin in the cells. Suspending sickle cells in a hyperosmolar medium increases the intracellular hemoglobin concentration as the cell is dehydrated. This phenomenon may account in part for sickling in renal papillae.89,90 Conversely, any agent that causes increased red cell volume will retard the sickling process by decreasing the MCHC. Marked dehydration results in both vascular stasis and hypertonicity and can precipitate a crisis.
Blood Flow in the Microvasculature In the last analysis, vasoocclusion is the result of a variety of factors on blood flow in the microvasculature. The factors that influence the rheologic properties of blood that contains sickle cells are extremely complex. For example, shear stresses, such as those that occur in the circulation, serve to break down gel structure.91 However, this results in the creation of more nucleation centers and results in a decrease in the delay time. In the circulation, flow properties of blood are influenced not only by factors such as the rigidity of the erythrocytes but also by the adherence of sickle cells to the endothelium,92 which may involve band 3,93 and to each other.94 Variations in such factors, modifying the rheologic consequences of the sickling process, undoubtedly play a role in determining when vasoocclusive episodes will occur. Granulocytes, too, manifest increased adherence to endothelium, and this has been attributed to increased expression of CD64.95
The sequence of events that leads to occlusion of blood vessels by sickle cells is thus complex.96,97 One essential factor is the aggregation of sickle hemoglobin, with the consequent changes in the rheologic properties of the erythrocytes (see “Biochemical Basis of Sickling,” above). The overall viscosity of the blood is a function of the hematocrit, and occlusion is more likely when hematocrit levels are relatively high. Adhesion of sickle cells to the vascular endothelium is an important factor and may be related to exposure of vascular endothelial adhesion molecules such as VCAM-1 (vascular cell adhesion molecule-1) and to the levels of plasma factors that enhance adhesion, including fibrinogen, factor VIII, fibronectin, von Willebrand factor, and thrombospondin. The adhesion receptors VLA-4 and CD36 are found in unusually high numbers on sickle cell reticulocytes, and they help to mediate adhesion of sickle RBC to endothelium.98 Abnormalities in nitric oxide–induced vascular relaxation has also been indirectly implicated. Leukocytes probably also participate in this complex process, perhaps by releasing cytokines that upregulate adhesive endothelial glycoproteins, and it has been suggested that a part of the therapeutic effect of hydroxyurea may be related to reduction of the leukocyte count.99
Infections It is a common clinical observation that vasoocclusive crises may be precipitated by infections. In many cases the mechanism by which infection increases sickling is easily discernible: fever, vomiting, and diarrhea may produce dehydration; lack of food intake may produce acidosis; and hypoxemia may result from pneumonia. It is quite possible that other, more subtle mechanisms may also be responsible for precipitation of crises in patients with sickle diseases with infections.
A patient with sickle cell anemia is homozygous for the gene for sickle hemoglobin and has therefore inherited one abnormal gene from each parent. If 7.8 percent of a population are sickle cell trait carriers,73 as in the African American population, there is a 1:164 chance that two carriers will marry, and the chances that an offspring of such a marriage will have sickle cell anemia is 1:4. In such a population, about 1 in 650 will have sickle cell anemia.
Similarly, persons with hemoglobin SC disease must have one parent with a sickle hemoglobin gene and another with a hemoglobin C gene. Since these genes are allelic b chain mutations, persons with hemoglobin SC disease have no normal b polypeptide chain gene and therefore have no hemoglobin A. The carrier rate for hemoglobin C in African Americans is about 2.3 percent.73 If 7.8 percent of a population carries the hemoglobin S gene, then the probability of a sickle cell trait and hemoglobin C trait mating is about 1 in 280, and therefore 1 in about 1120 newborns will inherit hemoglobin SC disease. The same principles apply for inheritance of sickle cell b-thalassemia, since the b-thalassemia gene is also allelic to the gene for sickle hemoglobin. In African Americans the frequency of b-thalassemia is approximately 0.8 percent,100 so that the expected birth frequency of sickle cell b-thalassemia is about 1 per 3200.
Hemoglobin S occurs with greatest prevalence in tropical Africa; the heterozygote frequency is usually about 20 percent, but in some areas it reaches 40 percent. The sickle cell trait has a frequency of about 8 percent in the African American populations. The sickle cell gene is found to a lesser extent in the Middle East, in Greece, and in aboriginal tribes in India (Fig. 47-3). On occasion sickle cell disease is found in people of European extraction, especially where racial admixture has occurred over the centuries.101

FIGURE 47-3 Distribution of sickle cell gene in Africa and Asia. (Allison,453 by permission.)

The high prevalence of the gene for sickle hemoglobin in areas of the world where malaria has been common suggests that persons with sickle cell trait have a selective advantage over normal individuals when they contract this disease.102 This advantage seems to be restricted to young children with sickle trait and Plasmodium falciparum infection. Although children with sickle cell trait are readily infected by P. falciparum, the parasite counts remain low. It may be that the infected red cell is preferentially sickled and destroyed, probably in the vascular system of the liver or spleen, where oxygen tensions are low and phagocytic cells abound. Whatever the mechanism, the result is that the infection is of short duration and the incidence of cerebral malaria and death is low.
At one time one could only speculate as to whether the sickle cell mutation had arisen only once and had gradually gained a worldwide distribution or whether the same mutation had arisen independently in various populations and then been the subject of selection, presumably through a protective effect against malaria. The ability to detect mutations in nontranscribed portions of DNA adjacent to the b-globin gene (see Chap. 9) has now provided insight into this problem. Such mutations are so close to the b-globin gene that the probability of a crossover (see Chap. 9) is vanishingly small. Thus, the relationship of the two mutations to one another will persist through hundreds of generations, permitting one to trace population movements. When the b-globin gene cluster is digested with restriction endonucleases, five distinct patterns are found in association with the sickle mutation. Four of these occur in Africa and have been designated the Senegal, Benin, Bantu, and Cameroon types.103 An additional haplotype is typical of the Indian subcontinent.104 These findings suggest that the sickle mutation arose independently at least five times.
Hemoglobin DPunjab, now recognized to be identical with hemoglobin DLos Angeles, both having the structure a2b2121 Glu®Gln, also interacts with hemoglobin S in forming aggregates in the deoxy conformation. Hemoglobin SDPunjab/Los Angeles disease is a relatively severe sickle cell disease.105 This hemoglobin is found in frequencies of approximately 3 percent in Northwest India; however, it is relatively rare in populations of African origin, and hemoglobin SD disease is therefore very uncommon.
Although we regard sickle cell anemia as the prototype of the sickle cell diseases, in the African American population only about one-half of the patients with sickle cell diseases have sickle cell anemia (homozygous SS disease). This fact is important from the point of view of genetic counseling: about half of all children with sickle cell disease arise from matings in which only one of the parents carries the sickle cell gene. Moreover, since early mortality rates are probably higher in sickle cell anemia than in the other sickle cell diseases, an even smaller proportion of adults with these sickle cell diseases are actually homozygous for hemoglobin S.
No naturally occurring animal models of sickle cell disease have been described. Some deer have red cells that undergo sickling when oxygenated,106 but not under physiologic conditions of pH and PO2. Cells from patients with sickle cell anemia have been infused into rats,107 and this model system has been used to study the effect of various therapeutic agents. However, this approach is limited by the short time that the cells survive in the circulation of the heterologous species. The development of transgenic technologies (see Chap. 9) has made it possible to produce mice whose red cells carry a high percentage of sickle hemoglobin.108 Notably, by combining the sickle b-globin transgene and human a-globin genes with knockouts of murine globin genes109 or thalassemic mutations,110 mice that have many of the features of human sickle disease have been produced.
The newborn infant is protected by the high level of fetal hemoglobin in the red cells during the first 8 to 10 weeks of life. As the level declines the clinical manifestations of sickle cell disease appear, and the hematologic manifestations of sickle disease are apparent by 10 to 12 weeks of age.111
Many patients with sickle cell anemia are in reasonably good health much of the time, achieving a steady-state level of fitness. This state of relative well-being is periodically interrupted by a crisis that may have a sudden onset and occasionally a fatal outcome. The early recognition and subsequent clinical assessment of sickle crises are greatly facilitated by familiarity with the patient’s steady state.
Various types of crises occur, and these may be classified as follows: vasoocclusive (painful) crisis, aplastic crisis, sequestration crisis, and hemolytic crisis.
Vasoocclusive Crisis The vasoocclusive crisis is the most common and is the hallmark of the patient with sickle cell disease.112 The frequency with which such crises occur varies from almost daily to less than once yearly. The vasoocclusive crises result from complex interactions between endothelium, plasma factors, leukocytes, and rigid, sickled red cells leading to the obstruction of blood vessels (see “Blood Flow in the Microvasculature,” above). Tissue hypoxia occurs and ultimately leads to tissue death and localized pain. It is important to distinguish the pain of a vasoocclusive crisis from the pain caused by other, sometimes more treatable disorders. Appendicitis must sometimes be considered, but it is notable that it has been suggested that the incidence of appendicitis is lower in patients with sickle cell diseases than in the general population.113 Fever is often present, even in the absence of demonstrable infection. Sickle cell crisis is, to a large extent, a diagnosis by exclusion.114 Vasoocclusive crises may affect any tissue, but the pain occurs especially in bones, chest, and abdomen. Infarctions in the spleen, which may be a cause of abdominal pain, are so common in sickle cell anemia that after age 6 to 8 the spleen usually becomes very small because of scarring111 (autosplenectomy). Myonecrosis is unusual but has been documented.115
Infarction of cerebral vessels, leading to stroke, is the most serious type of vasoocclusive complication (see “Other Clinical Manifestations, Central Nervous System,” below).116
Aplastic Crisis Aplastic crises in sickle cell disease are of the type familiar in patients with other hemolytic disorders, in which the reticulocyte count falls to low levels, indicating that red cell production has decreased dramatically. Depression of erythropoiesis is generally associated with infections. Infections with the B19 strain of Parvovirus appear to be by far the most important cause of such crises117,118 and 119 and may be accompanied by extensive marrow necrosis.120,121 Because of the short red cell life span in sickle cell disease, even in the steady state, a temporary depression of marrow activity can cause a catastrophic fall in hemoglobin level, manifesting as an aplastic crisis. Marrow output failure may also result from a deficiency of folic acid, especially during late pregnancy, and this has sometimes been designated a megaloblastic crisis.
Sequestration Crisis The sequestration crisis occurs particularly in infants and young children,122 although it may occur in adults with splenomegaly, particularly those with hemoglobin SC disease or sickle b-thalassemia.123,124 It is characterized by sudden massive pooling of red cells, especially in the spleen. Hypovolemic shock and cardiovascular failure may develop rapidly.122 A major acute sequestration crisis is considered to be one in which the hemoglobin level is less than 6 g/dl and has fallen more than 3 g/dl when compared with the baseline value; a minor acute sequestration crisis is one in which the hemoglobin level is higher than 6 g/dl.125 In a study of children with sickle disease born in Los Angeles in the 1960s and 1970s, such crises were responsible for 10 to 15 percent of deaths in the first 10 years of life.111
Hemolytic Crisis The red cell life span is shortened in all the varieties of sickle cell disease. It may suddenly be further reduced, probably for a variety of reasons. This increased rate of hemolysis is designated a hemolytic crisis. The resulting increase in jaundice is associated with a falling hemoglobin and an elevated reticulocyte count. Such crises are very rare; in most instances changes regarded as due to increased hemolysis represent some other complication of sickle cell disease.126 It has been suggested that concurrent G-6-PD deficiency may be a factor leading to hemolytic crises,77 but it seems unlikely that this is actually the case, since the young red cell population of patients with sickle cell disease has normal or near-normal G-6-PD activity even when G-6-PD deficiency is present.
An increase in the level of jaundice is not necessarily an indication of increased hemolysis (see “Other Clinical Manifestations, Liver,” below). Other causes for jaundice, such as hepatitis, cirrhosis, and gallstones, should be sought. Patients with a chronic hemolytic anemia are especially likely to form bilirubin stones, which may cause extrahepatic biliary obstruction.
Growth Young children with sickle cell anemia tend to be shorter than normal.127,128 Puberty is delayed, but considerable growth occurs in late adolescence, so that adults with sickle cell anemia are at least as tall as normal.128
Bony Abnormalities The chronic hemolytic anemia with erythroblastic hyperplasia will result in widening of the medullary spaces, thinning of the cortices, and sparseness of the trabecular pattern.129 Although these changes are recognizable in the skull, they are usually not as marked as the typical “hair-on-end” appearance characteristic of the patient with b-thalassemia major (see Chap. 48). The vertebral bodies may show biconcavities of the upper and lower surfaces (codfish spine). Pressure from the nucleus pulposus into an area of bone infarction may result in steplike depressions—as if a coin had been pushed into the vertebral body. This x-ray picture is highly suggestive of sickle cell disease.
Crisis with bone pain may be followed by the appearance of periosteal reaction, and irregular areas of osteosclerosis may be seen, representing areas of bone infarction. Bone scans with 99mTc are not helpful in delineating areas involved in painful crisis.130 However, magnetic resonance imaging seems more promising.131,132 and 133
Sickle cell dactylitis is probably due to limited avascular necrosis of marrow. Nearly one-half of children with sickle cell anemia suffer from this painful disorder, manifesting swelling of the dorsal surfaces of the hands and/or feet (Fig. 47-4). Dactylitis occurs almost entirely in the first 4 years of life, with a peak incidence at about 1 year.134 Environmental cold is considered to be an important precipitating factor.

FIGURE 47-4 Sickle cell dactylitis (hand-foot syndrome). Note the swelling of the right hand involving the thumb and first and second fingers. (Diggs,454 by permission.)

In later life necrosis of the head of the femur due to infarction of the nutrient artery is common and may be responsible for severe pain and serious disturbances of gait. Osteonecrosis of the head of the humerus occurs in about 5 percent of patients with sickle disease. Although the incidence in various genotypes is the same, onset tends to be earliest in those with the SS genotype, latest in those with sickle cell b-thalassemia, and intermediate in those with SC disease.135,136 Chondrolytic arthritis has also been observed.137 The bone manifestations of sickle cell disease may closely mimic osteomyelitis or arthritis. Ultrasonography may be helpful in making the distinction between infarction and infection.138
The presence of necrotic marrow may favor the development of infection, especially with Staphylococcus aureus139 and Salmonella140 (Fig. 47-5). Necrotic marrow may also embolize the lung, producing the “chest syndrome” or in some cases sudden death.141

FIGURE 47-5 Salmonella typhimurium osteomyelitis in a patient with hemoglobin SC disease. (River et al,455 by permission.)

Genitourinary System The renal medulla is an area that is particularly susceptible to damage in sickle cell disease.142 Its unique environment, characterized by anoxia, hyperosmolarity, and low pH, predisposes to sickling. Indeed, the kidney is highly susceptible to the effects of the sickling phenomena and is the only organ commonly affected in the generally benign sickle cell trait. The ability to concentrate urine is lost in patients with sickle cell trait as well as those with sickle cell disease.143 Infarctions may also occur, with renal papillary necrosis (Fig. 47-6) both in patients with SS disease and patients with sickle cell trait.144 Approximately 50 percent of patients with sickle cell anemia have enlarged kidneys as judged by radiologic examination, and calyceal abnormalities of various types are common.145 Renal failure is a late complication of sickle cell disease.146 In one study an increased incidence of renal carcinoma was observed in patients with sickle cell disease.147

FIGURE 47-6 Renal papillary necrosis in a patient with sickle cell trait. Note the small medullary cavities in the upper three calyces of the left kidney (arrows). (Harrow et al,456 by permission.)

Priapism is a serious complication of sickle cell disease.148,149 and 150 It is more common in patients with the SS genotype than in other sickle disease genotypes. It often results in permanent impotence in adults. Prepubertal males have shorter episodes and a good prognosis for future erectile function.
Underdeveloped genitalia and hypogonadism may occur, and it has been suggested but not proven that this could be due to zinc deficiency.151,152
Spleen Splenomegaly is prominent in early childhood, but splenic function is impaired,153 and presumably as a result the incidence of bacteremic infections is high.154 Infections of the splenic remnant itself, sometimes with abscess formation, have been documented.155,156 In adults in the United States splenomegaly is uncommon because of splenic fibrosis. Repeated infarctions of the spleen lead to fibrosis, calcifications, and autosplenectomy. However, in U.S. patients with sickle cell diseases other than SS disease, i.e., sickle cell thalassemia or hemoglobin SC disease, splenomegaly commonly persists into adult life. In Africa, probably as a result of infection with organisms such as Plasmodium, splenomegaly is observed in almost one-quarter of patients with SS disease.157
Liver Jaundice and hepatomegaly are common in sickle cell anemia.158 The liver may be enlarged, sometimes extending to the iliac crest, particularly in young children and again in middle age, at which time there may be evidence of hepatic dysfunction. The small number of sickled cells found in the hepatic vein after passage through the liver suggests that the cells most susceptible to sickling are trapped by their rigidity and engulfed by phagocytes during their passage through the hepatic sinusoids, where the oxygen content of the blood is extremely low. The liver may transiently increase in size during a painful crisis.159 Sickle cell intrahepatic cholestasis is a rare, catastrophic complication. Characterized by sudden onset of right upper quadrant pain, progressive hepatomegaly, and a serum bilirubin level that may rise to well over 1700 µM (100 mg/dl), its outcome is usually fatal, although recovery has been reported after exchange transfusion.160 In sickle cell disease, excretion of urobilinogen is usually greater than normal. Some 50 to 70 percent of adult patients may have bilirubin gallstones,161 and gallstones have also been found in children as young as 6 years of age.162 Patients who have received transfusions may develop hepatitis that is sometimes mistaken for a hemolytic crisis. While about one-third of patients with sickle cell disease manifest liver dysfunction,163 the cause is multifactorial.161,163,164 and 165 Excess iron deposition is common, but frank hemochromatosis is only occasionally encountered. 164,165,166,167 and 168 Some patients with chronic jaundice that seems out of keeping with the degree of hemolysis may have inherited a common mutation in the promoter of the UDP glucuronosyl transferase gene that is known to cause Gilbert disease and increases the jaundice found in patients with thalassemia and G-6-PD deficiency.169,170
Cardiopulmonary System The heart is frequently the site of some of the most prominent physical findings in sickle cell disease.171 During crisis, striking tachycardia may occur because of the combination of fever and anemia. The precordium demonstrates the overactivity similar to that seen with marked hyperthyroidism. The point of maximal impulse is usually forceful and pounding in nature, and the heart is frequently enlarged to both the left and the right. Systolic and diastolic flow murmurs are often heard.
The blood pressure of patients with sickle cell anemia and to a lesser degree with SC disease is significantly lower than published norms for age, race, and sex, a difference that increases with age.172 Stroke was associated with higher systolic but not diastolic pressures.
Pulmonary infarctions are common in persons with sickle cell disease and may lead to repeated episodes of chest pain, unexplained dyspnea, or “atypical pneumonia.” A combination of fever, chest pain, rise in the white count, and appearance of a pulmonary infiltrate in patients with sickle diseases is referred to as the acute chest syndrome.173 Age has been found to exert a marked effect on the clinical picture of acute chest syndrome. In children, acute chest syndrome is milder and more likely due to infection, whereas in adults it is more likely to be severe and to be associated with pain and a higher mortality rate. The clinical and roentgenologic features observed in these patients do not aid in differentiating pulmonary infarction from pulmonary infection, but thin section CT may be more helpful.174 Rib infarctions are commonly observed on bone scan, and it has been suggested that they may play a role in the pathogenesis of the acute chest syndrome.175 This disorder is regarded as being multifactorial, with infection, infarction, and pulmonary fat embolism all being factors that may play a role.176
The combination of increased flow rate and pulmonary vascular occlusions may result in increased pulmonary pressure and eventually cor pulmonale.177 Systemic marrow fat embolism has been associated with pulmonary hypertension.178 However, it has been suggested that patients with recurrent episodes of the acute chest syndrome are not particularly prone to develop pulmonary hypertension.179
Eye Retinal vessel obstruction is followed by neovascularization with arteriovenous aneurysms. These may eventually result in hemorrhage, scarring, retinal detachment, and blindness.180 These changes occur at the periphery and may initially be difficult to visualize through an ophthalmoscope, even with a fully dilated pupil. At the early stage of retinal disease, vision is therefore not impaired. The retinal changes, collectively termed “sickle retinopathy” have been divided into nonproliferative and proliferative groups. Nonproliferative changes include so-called “salmon patch” hemorrhages, iridescent spots, and black sunbursts. The latter term is used to describe lesions that occur in the peripheral retina; as the retina becomes ischemic, neovascular growth starts at abnormal arterial venous anastomoses resulting from vascular occlusions. These vascular growths extend toward the periphery. Because these abnormal vascular fronds resemble the marine invertebrate Gorgonia flabellum, the lesions are called “sea fans.”
Examination of the conjunctiva may reveal multiple short comma-shaped capillary segments that often appear isolated from the vascular network because the afferent and efferent lumens are empty. These transient sites of tightly clumped intravascular erythrocytes are found on the bulbar conjunctiva underneath the eyelids (Fig. 47-7). They occasionally disappear during the course of a lengthy examination because of the warmth of the light. Visual loss is most common in SC disease and is due principally to vitreous hemorrhage, secondary to bleeding from the neovascularized areas.

FIGURE 47-7 Lower bulbar conjunctiva in a patient with sickle cell anemia, showing many segmentations. (Paton,457 by permission.)

The orbital compression syndrome, consisting of fever, headache, orbital swelling, and optic nerve dysfunction, has been documented in a number of patients with sickle cell disease.181 The most common cause appears to be orbital marrow infarctions.
Central Nervous System Cerebrovascular accidents are one of the most devastating complications of sickle cell disease. Once thought to be due to obstruction of small blood vessels, it now appears to be due to lesions of major vessels, particularly the internal carotid and anterior and middle cerebral arteries.116,182 Even children with no history of stroke may show evidence of infarction on MRI.183 The prevalence of cerebrovascular accidents has been found to be 4.01 percent and the incidence 0.61 per 100 patient-years in sickle cell anemia (SS) patients, but cardiovascular accidents occur at somewhat lower frequencies in all common genotypes.184,185 and 186 Stroke has even been reported in more than a dozen children and adults with sickle trait, but the cause-and-effect relationship must be considered unproven.187,188 The incidence of infarctive cerebrovascular accidents is lowest in sickle cell anemia patients 20 to 29 years of age and higher in children and older patients. On the other hand, the incidence of hemorrhagic stroke in SS patients is highest among patients aged 20 to 29 years. The mortality rate was 26 percent in the 2 weeks after hemorrhagic stroke. No deaths occurred after infarctive stroke.184 The incidence of stroke among patients with hemoglobin SC disease is significantly lower, approximately 2 percent.184,185 and 186 Measurement of the velocity of cerebral blood flow by transcranial Doppler ultrasonography has some predictive value with respect to the probability of developing a stroke. 189 In most patients the stroke occurs without any warning, but in about one-quarter of the cases the stroke occurs in the context of some other complication, such as a painful crisis, priapism,186 or an aplastic crisis.190 Risk factors include low steady-state hemoglobin, previous transient ischemic attacks, occurrence of priapism,184,191 and increased plasma homocysteine levels.192 Preliminary studies suggest that the inheritance of the prothrombin Leiden mutation and the 677C®T mutation in the methylenetetrahydrofolate reductase (MTHFR) are not major factors in the development of strokes.193,194 Recurrence of strokes is a prominent feature of this complication; at least 67 percent of patients who have one stroke will suffer at least one more if untreated. Such episodes are particularly common within the first 36 months after a stroke.185
Many other neurologic symptoms have been described, including drowsiness, coma, convulsions, headache, temporary or permanent blindness, cranial nerve palsies, and paresthesias of the extremities.195 Multiple cerebral aneurisms appear to be more common in patients with sickle cell disease.196,197
Leg Ulcers Although encountered in patients with other types of hemolytic disease, ulcers around the ankles are a particularly common feature of sickle cell disease.198,199 They are unusual in the younger child, and stasis clearly plays some part in their formation. They usually start as a small break in the skin or a blisterlike area that breaks down and rapidly extends to form a painful, indolent ulcer. Usually the ulcers become infected, and the base is covered with a yellow, purulent layer. They may extend deeply enough to expose muscle. Once formed, leg ulcers do not heal spontaneously, and they become a major source of morbidity for affected patients.
Infections Patients with sickle cell disease are particularly prone to develop infections, and this may be the single most common reason for hospitalization.200 Because of functional asplenia, impaired phagocytic function,201 and a defect in activation of the alternate complement pathway, infections may be quite hazardous, particularly so in children. The risk varies significantly from patient to patient, with some patients having very few infections. Pneumonia seems to be the most common infection encountered and often is of pneumococcal origin, particularly in children. As noted above, osteomyelitis due to Staphylococcus and to Salmonella also is relatively common.139 Babesiosis has been reported to occur in one patient,202 possibly as a result of the impaired splenic function.
Pregnancy Pregnancy in women with sickle cell anemia is accompanied by an increased incidence of pyelonephritis, pulmonary infarction, pneumonia, acute chest syndrome, antepartum hemorrhage, prematurity, and fetal death.203 Megaloblastic anemia responsive to folic acid, especially in late pregnancy, also occurs with increased frequency. The birth weight of infants of mothers with sickle cell anemia is below average,204,205 and the fetal wastage is high.206,207 The cause of neonatal death is obscure, but it may sometimes result from vasoocclusion of the placenta204; the postmortem findings are those of intrapartum anoxia.208 The maternal mortality in sickle cell disease was formerly prohibitively high, with rates averaging 33 percent, but is now much lower, averaging about 1.5 percent in various series.206,207,209,210,211,212 and 213 Higher mortality rates are still observed in some parts of the world, however, with maternal mortality rates of up to 9.2 percent and a perinatal mortality of up to 19.5 percent.210,214,215
The steady-state hemoglobin level of patients with sickle cell anemia is usually between 5 and 11 g/dl. The anemia is normochromic and normocytic in spite of the elevated reticulocyte count.216 In comparison with patients with similarly increased reticulocyte counts, patients with SS disease may be considered to have a “microcytic” anemia, presumably because the sickle mutation impairs the efficiency of production of hemoglobin. The range of red cell densities is increased in sickle cell anemia,217 but the average cellular MCHC is normal. In SC disease, however, the average MCHC is increased.217 Erythropoietin levels may be reduced relative to the degree of anemia218 but have also been reported to be appropriate.219 The anemia is accompanied by laboratory signs of hemolysis, with increased indirect-reacting serum bilirubin and reticulocytosis and often circulating nucleated red cells. As in any hemolytic anemia, endogenous CO production is increased220,221 and haptoglobin absent. Sickled erythrocytes are often evident on inspection of the blood film. Target cells may be present, particularly in sickle cell–hemoglobin C disease and in sickle cell b-thalassemia. In sickle cell hemoglobin C disease, folded cells are sometimes seen (Fig. 47-8, Fig. 47-9). Examination of the red cells by inference phase-contrast microscopy reveals surface indentations, presumably resulting from splenic hypofunction, in approximately 20 percent of the cells.153 A modest polymorphonuclear leukocytosis with a left shift is common even in the steady state 222,223 and may be due in part to redistribution of leukocytes from the marginal to the circulating granulocyte pool.222 It does not necessarily signify an infection. Thrombocytosis is also common, but evidence of intravascular coagulation with thrombocytopenia has been noted rarely during crisis.224

FIGURE 47-8 Scanning electron microscopy of individual SC cells: (1) multifolded cells; (2) unifolded cell resembling pita bread and most likely the same as the “fat cell” shown in Fig. 47-9; (3) tridimpled cell, also called a triangular cell. (Lawrence et al,52 by permission.)

FIGURE 47-9 Bizarre-shaped erythrocytes in the blood film of patient with hemoglobin SC disease. (A) “Fat sickle cells.” (B) Crescent-shaped erythrocyte with three deep-hued crystals (center left). Two bizarre condensed hemoglobin masses in a red blood cell (lower right). (C) Elongated red corpuscle with concentration of hemoglobin at each end and hemoglobin-free central area (center). (D) Red cell with two parallel, dark, crystal-like structures of different lengths, terminating in a pyramid tip (center). (E) Erythrocyte with two parallel formations separated by a clear area (upper right). Red cell with one elongated mass (lower left). (F) Erythrocyte with densely stained hemoglobin masses (upper right). Red cell with one dark, elongated, rounded bulge and one small triangular hemoglobin mass, leaving two areas relatively free of hemoglobin (lower left). (Diggs and Bell,458 by permission.)

The marrow shows erythroid hyperplasia. Immunoglobulin levels are frequently increased. IgA levels are particularly elevated in all forms of sickle cell disease. Elevations of IgG levels are also sometimes seen, while IgM levels appear to be elevated particularly in patients with sickle cell thalassemia and in individuals with other combinations such as hemoglobin SC disease.225 A decreased number of T lymphocytes and increased B lymphocytes in the blood have been reported.226 Activation in the alternative complement pathway has been detected in some patients227 and is apparently a result of phosphatidylserine exposure by erythrocytes.228 This may be responsible, in part, for increased susceptibility to infection.
Plasma tocopherol229 and zinc230,231 levels are often low, the latter possibly due to zincuria.151,231 Serum ferritin levels are normal in the first two decades of life but tend to rise in older patients, and modest elevations in plasma iron content are also frequently encountered.232 High ferritin levels and increased iron burden occurs in patients who receive chronic transfusion therapy, and such patients are often treated with desferrioxamine.233,234 and 235 However, although the development of hemochromatosis has been reported,165 this seems to be a relatively uncommon complication, even in extensively transfused patients. Frank iron deficiency is not rare, and overt iron deficiency with microcytosis has sometimes been observed in patients with sickle cell anemia.236,237 Thus, the presence of microcytosis does not necessarily indicate the concurrent presence of thalassemia.
Diagnosis depends upon documentation of the presence of sickle hemoglobin, preferably by electrophoresis.233 Many different media and buffers are used to distinguish different mutant hemoglobins from one another, but several relatively simple systems suffice for the differentiation of most variants from one another.238 Rapid methods that are less reliable for the detection of sickle hemoglobin include the observation of sickling of red cells containing sickle hemoglobin microscopically under a coverslip by suspending the cells in a droplet of a 2% solution of sodium metabisulfite239 and solubility tests. The latter depend on the low solubility of reduced sickle hemoglobin which results in the development of turbidity under appropriate conditions.240 However, such tests do not detect hemoglobin C or b-thalassemia and do not reliably distinguish between sickle trait and sickle disease and are therefore of limited value. With the refinement and automation of techniques it has also been possible to detect sickle hemoglobin accurately and economically by high-pressure liquid chromatography and by isoelectric focusing.241 Use of the polymerase chain reaction to detect the sickle mutation is the method of choice for prenatal diagnosis.242
Because there are no normal b polypeptide chain genes, patients with sickle cell anemia or hemoglobin SC disease have no normal adult hemoglobin. In the heterozygote for the sickle cell gene and bo-thalassemia no hemoglobin A is found, but small amounts of normal hemoglobin are present in the compound heterozygote for the sickle cell and b+-thalassemia genes. The concentration of fetal hemoglobin usually is increased in sickle cell b-thalassemia and is heterogeneously distributed among the red cells. The quantitation of hemoglobin A2 is of value in differentiating sickle cell anemia from sickle cell bo-thalassemia; hemoglobin A2 levels tend to be increased in the latter condition. Family studies are particularly helpful if sickle cell bo-thalassemia is to be clearly differentiated from sickle cell anemia.
Sickle cell anemia can be diagnosed at birth by subjecting cord blood samples to electrophoresis.243 Ideally, all babies of ethnic groups with a high frequency of the sickle cell gene should be screened at birth, because of a demonstrated decrease in mortality of very young children when the diagnosis is made.244 The cost-effectiveness of screening depends on the composition of the target population; it has been estimated to be $206,000 per death averted in Alaska. Screening is particularly desirable if the mother has sickle cell trait.
Chorionic villus biopsy has been used extensively to obtain fetal DNA for diagnosis in the first trimester.245 The availability of techniques for the amplification of genomic DNA makes feasible DNA-based prenatal diagnosis of sickle cell disease (see Chap. 9 and Chap. 46). The mutant and normal sequences can be differentiated with an appropriate restriction endonuclease or by the use of synthetic oligonucleotide probes.242,246
An authoritative guide for the management of patients with sickle cell diseases has been published under the auspices of the Heart, Lung, and Blood Institute of the National Institutes of Health.233
General Measures Since no fully satisfactory, specific treatments for the sickle cell disorders have yet become available, physicians must concentrate their therapeutic efforts in the direction of continuous and effective general medical care and appropriate management of complications as they arise.247,248 Folic acid supplementation has been suggested, but there is little evidence that it is beneficial249 except in pregnancy and in patients with other disorders that increase the requirement for folate. Transfusions are not usually required, except in special circumstances such as stroke, abnormal transcranial Doppler findings, leg ulcers, or intractable or frequently recurring painful crises.250 Prophylactic transfusion does, as expected, decrease the frequency of crises,166 but it requires administration of desferrioxamine to prevent iron overload and subjects patients to the risk of the complications of transfusion such as alloimmunization251 and transmission of infection. A randomized double-blind study showed that conservative transfusion therapy (designed to keep the hemoglobin level over 10 g/dl) was as effective in preventing perioperative complications as more aggressive therapy (designed to maintain the hemoglobin S level under 30%) and was safer.252 Acute neurologic symptoms have been reported to occur after partial exchange transfusion, but a cause-and-effect relationship is not established.253 The use of neocytes (young erythrocytes; see Chap. 140) is probably not justified because of inconvenience and high cost.
Exposure to cold and high altitudes should be avoided. Special vocational training of patients with sickle cell anemia for suitable occupations is useful. It is important that patients live as normal a life as possible. Occupations that do not require heavy manual labor and in which occasional absences from work are practical may be excellent and can make these patients productive members of society.
Acute Chest Syndrome Rapid and correct diagnosis is of paramount importance. It has been recommended that if normal flora are seen on gram-stained sputum in a patient who is not seriously ill with the acute chest syndrome, no antibiotics should be used. However, more symptomatic patients with sputum production should receive antibiotics based on the organisms found in the gram-stained sputum. In adults, in contrast to children, such pulmonary events rarely appear to be due to infection with pneumococci.254 Because of the life-threatening nature of the acute chest syndrome, some clinicians prefer a more aggressive approach, immediately instituting empiric antibiotic therapy including erythromycin because of the frequent involvement of bacteria such as Chlamydia or Mycoplasma.176 Adequate hydration is important, but fluid overload resulting in pulmonary edema occurs not infrequently, and thus careful monitoring of fluid balance is required.176 Exchange transfusion has been advocated.255
Infections The administration of pneumococcal vaccine is recommended,256 but a number of failures of the vaccine to protect children with sickle cell disease against infection with the pneumococcus have been reported, and children with sickle disease should receive pneumococcal vaccine and penicillin prophylaxis at least until the age of five.233,257,258 and 259 Other infectious diseases against which patients with sickle diseases should be immunized include hepatitis B, diphtheria, tetanus, pertussis, poliomyelitis, and Haemophilus influenzae.233 Infections should be treated vigorously with antibiotics. Because patients with sickle cell anemia are unable to concentrate urine adequately, dehydration during the course of infection represents a special risk to be avoided by adequate fluid administration.
Crises Once a small blood vessel is totally obstructed by sickled cells in the development of a painful crisis, the obstruction is probably irreversible. Yet the function of neighboring blood vessels in the areas obstructed by rigid sickled cells may be preserved by a number of therapeutic measures. The patient should be kept warm, and adequate hydration should be maintained by the oral or intravenous route. The role of oxygen therapy in the treatment of vasoocclusive crises is poorly defined. Although the administration of oxygen was once considered to be contraindicated because of a putative negative effect on erythropoiesis, it seems doubtful that it does any harm aside from the minor discomfort incident to its administration, and it may be useful in patients with a decreased arterial oxygen saturation. Hyperbaric oxygen usually fails to benefit the patient,260 although occasional success using this treatment has been claimed.261
The anticoagulants dicumarol262 and the defibrinating enzyme Arvin263 have been tried without success. Intravenous administration of magnesium sulfate264 has been reported to be beneficial, although a therapeutic effect has not been confirmed.265 Promising results of the treatment of sickle crisis with pentoxifylline, a drug reported to increase erythrocyte deformability, were reported in a double-blind study266 but could not be confirmed.267 Oral sodium bicarbonate or sodium citrate therapy has been tried in the treatment of an established vasoocclusive crisis, as well as in its prevention,265 but the efficacy of this treatment could not be confirmed in a controlled study.268
Management with analgesics of the pain of infarctive crises represents a particularly difficult problem for the physician233,269 and is discussed in Chap. 21. In most instances the manifestations of vasoocclusive crisis may gradually disappear over a period of hours or days on symptomatic management.
Splenic sequestration crises are a life-threatening complication that must be treated vigorously. Transfusion with red cells (exchange transfusions if there is respiratory distress) and splenectomy (see below) have been recommended.122,125
Strokes Because of the high recurrence rates of strokes, special attention has been paid to this group of high-risk patients. Regular transfusion programs to maintain the sickle hemoglobin concentration at 30 percent of the total hemoglobin reduce recurrence rates.167 Allowing no more than 50 percent of the hemoglobin to be sickle hemoglobin may provide similar protection.270 A randomized study showed that transfusion greatly reduces the risk of a first stroke in children with sickle cell anemia who have abnormal results on transcranial Doppler ultrasonography.183,271
Hypersplenism and Splenectomy Because of “autosplenectomy,” hypersplenism is seldom a problem in sickle cell anemia. Hypersplenism may be suspected in other forms of sickle disease if a long-term transfusion program becomes necessary to maintain life or if leukopenia and thrombocytopenia are associated with a palpable spleen. Under these circumstances splenectomy may very occasionally be warranted. It has been recommended that splenectomy be performed in all children over the age of two in which one major or two minor splenic sequestration crises have occurred because of the danger of recurrent crises.125,233
Cholelithiasis It is useful to examine adolescent and adult sickle cell anemia patients for the presence of gallstones. It has been suggested that elective cholecystectomy be performed when stones are present,272 but since 50 to 70 percent of adult patients with sickle disease have been found to have gallstones,161 gallstones that do not cause symptoms should probably not be removed. Laparoscopic cholecystectomy has been found to be safe and cost-effective in children273 and adults.274
Contraception and Pregnancy Oral contraception may offer some additional hazard of thromboembolism in patients with sickle hemoglobin,275 but the risk is probably small compared to the risk of pregnancy itself. The contraceptives medroxyprogesterone acetate (Depo-Provera®) given parenterally monthly for 3 months and then every month or levonorgestrel + ethinyl estradiol (Microgynon 30®) given daily were associated with a decrease in the number of attacks of pain in one study.276
Although very high maternal mortality rates have been greatly reduced with good prenatal care, pregnancy and the postpartum period are still potentially hazardous for a mother with sickle cell disease.209 The patient should be closely supervised during pregnancy.277 Although prophylactic blood transfusions have been given to some patients with what appear to be satisfactory results,278,279,280 and 281 the effectiveness of this type of therapy is not proven.209,282 Studies demonstrating that exchange transfusions are not required have been presented283 and contested.280
Leg Ulcers Leg ulcers may respond to conservative treatment such as bed rest, elevation of the affected limb, zinc sulfate pressure dressings, or maintenance transfusion or may require surgical grafting.199 In a study of 172 patients,198 no difference in the rate of healing was associated with any of the different treatment modalities.
Bone and Joint Disease Joint replacement may be helpful to patients who have suffered osteonecrosis, but the number of complications and the number of revisions needed is extraordinary, so that the risk-to-benefit ratio is high.284 Core decompression has been found to be useful in the management of early avascular necrosis of the hip.285
Retinal Changes Vitreous hemorrhages and subsequent blindness may be the end result of the neovascularization that follows retinal infarction. Laser photocoagulation of new vessels may help to prevent this complication.180 When hemorrhages have occurred vitrectomy may be indicated. The administration of nifedipine seemed to improve conjunctival and retinal perfusion and color vision performance in patients with sickle cell disease.286
Priapism Surgical intervention is commonly practiced, particularly in postpubertal patients with priapism. However, there is no clear evidence of benefit from shunting procedures.148 Hydration and exchange transfusions have been associated with detumescence,150 and it has been suggested that the oral administration of the alpha-adrenergic agent etilefrine prevents recurrence of priapism.287 Penile prostheses have been found to be useful when impotence results from priapism.288,289
Anesthesia and Surgery The patient with sickle cell disease is at increased risk during anesthesia. If surgery is indicated, scrupulous care is needed to avoid factors known to precipitate crisis, including hypoxemia, dehydration, circulatory stasis, acidosis, cold, and infections.290,291,292 and 293
Preoperative transfusion with packed red cells may help to avoid complications in patients with sickle cell disease undergoing major surgery.294 Partial exchange transfusion has been advocated,166,295 and this has the advantage of immediate removal from the circulation of sickle cells that may obstruct the microcirculation. However, this more complex procedure probably has little if any advantage over simple transfusion if surgery is elective, as might be the case with patients requiring cholecystectomy or hip replacement.291 Exchange transfusion requires more blood to achieve an equivalent increment in the blood hemoglobin level, and therefore entails more risk than simple transfusion. Elevation of the hemoglobin level of the blood will markedly reduce the production of sickle cells by the marrow, and in view of the short life span of the patient’s own circulating erythrocytes, few sickle cells will remain in the circulation after a week or two. The complication rate of patients receiving exchange transfusions is, in point of fact, no lower than that observed in patients receiving simple transfusions.296 Exchange transfusion provides an advantage if iron overload is a concern or if removal of sickle cells is desired within a period of less than 5 to 7 days.
Transplantation Sickle cell disease is fundamentally a disease of the hematopoietic stem cell, and replacing the genetically defective cell with a normal one should cure the disease. One patient with sickle cell disease received a marrow transplant from a sib with sickle cell trait in the course of treatment of acute leukemia.297 As expected, the sickle cell disease was cured—converted into sickle cell trait.
Subsequently a considerable number of patients with sickle cell disease have undergone marrow transplantation. Groups in France and Belgium had transplanted 42 patients by 1992, with only 1 death; the other patients were alive with follow-ups of from 1 to 75 months.298,299 Over 90 percent of 50 patients transplanted in Belgium between April 1986 and January 1997 survived.300,301 In the United States an increasing number of patients are undergoing transplantation, and the overall results have been quite favorable.302 Twenty of 22 patients survived, with a median follow-up of 23.9 months (range, 10.1– 51.0), and 16 patients had stable engraftment of donor hematopoietic cells. In 1997 it was estimated that worldwide 140 patients had undergone transplantation.303
The decision of whether to transplant a patient with sickle cell disease is a difficult one, because the expected mortality rate for transplantation in young children with a good family donor match is still of the order of 10 percent, and the potential morbidity from chronic graft-versus-host disease needs also be taken into account. Thus, the initial focus must be upon those children with a poor prognosis, and apart from those who have already suffered a stroke, accurate prognostication is impossible.304,305 and 306
Agents with In Vitro Antisickling Activities For a number of years, attempts have been made to modify red cells containing hemoglobin S in a manner that will suppress the sickling process. Examples of this approach have included conversion of hemoglobin to carboxyhemoglobin307,308 and 309 or methemoglobin310; acetylation of the hemoglobin molecules with aspirin,311,312 methyl acetyl phosphate,313 or succinyldisalicylate314; cross-linking hemoglobin molecules with dimethyl adipimidate315,316; and use of carbonic anhydrase inhibitors to reduce the formation of H2CO3.317 Distilled water has been given intravenously to lower the MCHC.318 Glutamine has been given to change the oxidative state of the cell.319 Other antisickling agents that have been studied for a possible therapeutic effect include urea,320 cyanate,321 o-carbamoylsalicylates,322 methyl acetyl phosphate,323 lysyl-phenylalanine,324 procaine,325 zinc,326 pyridoxine327,328 and its derivatives,329,330 phenothiazines,331 steroids,315 nitrogen mustard,332 glyceraldehyde,333 hexamethylenetetramine,334 vitamin E,335 lawsone,336 substituted benzaldehydes,337 bepridil,338 and cetiedil.339 The usefulness of none of these has been confirmed.
Clinical Studies of Putative Antisickling Agents Most putative antisickling agents have been tested only with in vitro model systems, but a few have had clinical trials. The induction of methemoglobinemia310 by the administration of sodium nitrite or p-aminopropiophenone lengthened the life span of sickle cells, and the inhalation of carbon monoxide309 was found to have a similar effect. A patient with sickle cell anemia who was accidentally exposed to carbon monoxide levels presented with a hematocrit rising to 46 percent. A fatal outcome was attributed to extreme hyperviscosity occurring as the carboxyhemoglobin was converted to oxyhemoglobin and the cells again began to sickle.340 Pyridoxine,327 in contrast, did not influence red cell life span. The use of alkali to counteract the Bohr effect (the reduction of the oxygen affinity of hemoglobin at acid pH)341 has been thought to have some therapeutic value, but no beneficial effect could be demonstrated in controlled trials.342 The rationale for the use of urea was the ability of this chemical to dissociate hydrophobic molecular bonds and thus interfere with the sickling process. The concentration required to achieve such an effect cannot be reached in vivo, and clinical trials have proved disappointing.220 Carbamylation of the hemoglobin molecule by cyanate increases the affinity of the hemoglobin for oxygen.343 Because the sickling process requires the hemoglobin to be in the deoxy conformation, any agent capable of affecting the equilibrium between the oxy and deoxy conformations and thereby increasing the avidity of hemoglobin for oxygen must have an antisickling effect.86 Unfortunately, in clinical trials cyanate provoked polyneuropathy,344 retinal changes,344 and cataracts345 and therefore appears to be too toxic for systemic use. However, extracorporeal treatment with removal of excess cyanate by washing the red cells before returning them to the patient may overcome this problem.346,347 and 348 A number of substituted benzaldehyde compounds have been given experimentally to patients, producing a left shift in the oxygen dissociation curve and suggestive evidence of a decrease in hemolysis.337,349 It has been suggested that their effect may be due not only to stabilization of the oxy conformation of hemoglobin but also to decreasing potassium loss.337
Because sickling is highly concentration dependent, efforts to treat the disorder by swelling the red cells have been made. These have included the administration of distilled water intravenously318 and the lowering of serum sodium by the administration of a long-acting vasopressin derivative and vigorous hydration.350,351 The effectiveness and safety of the latter treatment has been questioned.352,353 Such treatment must still be regarded as experimental.
Increasing the Level of Fetal Hemoglobin Efforts have also been made to ameliorate the sickling process by stimulating the formation of fetal hemoglobin. Attempted originally by the administration of chorionic gonadotropin and estrogens,310 more recent efforts have focused on 5-azacytidine, a drug that inhibits the methylation of DNA and was shown to increase fetal hemoglobin concentrations of the red cells of baboons.354 The administration of 5-azacytidine to patients with sickle cell anemia resulted in an increased concentration of fetal hemoglobin355,356 and in a rise in the hemoglobin concentration of the blood.355,356 Other antineoplastic agents, including cytosine arabinoside357,358 and hydroxyurea357,359,360 and 361 or hydroxyurea in combination with erythropoietin,362 and erythropoietin alone363 also increase the fetal hemoglobin level. Butyric acid and related compounds364,365 and 366 increase fetal hemoglobin production in progenitor cells, experimental animals, and humans. However, isobutyramide given orally was not found to be useful.367 In vitro, interferon gamma has also been shown to increase fetal hemoglobin production.368
Of these agents, hydroxyurea is the one that has been tested most extensively and that has been introduced selectively into clinical practice. In a randomized study of 299 patients the median number of painful crises in patients given hydroxyurea was 2.5 per year, as compared with 4.5 per year in patients given placebo. Drug administration was started at 15 mg/kg body weight per day and was increased by 5 mg/kg/day every 12 weeks unless there were signs of marrow suppression.369 A number of open-label studies have been conducted and have in general shown a decrease in the incidence of painful crises370,371,372,373,374 and 375 without serious side effects. However, careful supervision is obviously required in the administration of a myelosuppressive agent. Compliance among children appeared to be very satisfactory in one study.376
Poloxamer 188, a nonionic surfactant with hemorheologic properties, has been tested in a double-blind randomized trial and found to decrease the severity of painful sickle crises.377
For a number of years it was unclear why sickle cell anemia was relatively common in African Americans and yet appeared to be a rare disease in Central Africa. Subsequently it was recognized that the early mortality associated with sickle cell anemia in Central Africa378,379 was responsible for its apparent rarity: the surveys of the distribution of sickle hemoglobin in Africa did not include the afflicted who had died. With good medical care, patients with sickle cell anemia usually survive to middle age.380,381 and 382 Assessment of the overall mortality of sickle cell anemia must take into account the fact that cases first diagnosed in late childhood, adolescence, or adult life are likely to result in a preponderance of the clinically more benign patients. In the two and one-half decades after 1968, mortality rates of African American children with sickle cell disease decreased considerably.383 In the 1–4 age group the mortality had fallen from 37 per thousand persons in those born between 1967 and 1969 to 22 per thousand among those born between 1986 and 1988. Corresponding figures for the 5–9 age group were 19 and 10 per thousand, and for the 10–14 age group 17 and 8 per thousand.383 These improvements in survival may probably best be ascribed to newborn screening programs,384 penicillin prophylaxis of disease caused by Streptococcus pneumoniae, and perhaps the use of pneumococcal vaccines. There were considerable regional differences. The mortality was considerably higher in Florida than in Maryland and Pennsylvania, probably related to the health care facilities available in different regions.385 Astonishingly, in California and Illinois, mortality from all causes among African American children born during 1990–1994 with SC disease was slightly less than overall mortality for all African American children born in the same time period.386
The manifestations of sickle cell disease vary with age.111 Acute manifestations often are associated with severe infections in childhood, while in the adult, symptoms are characteristically chronic and organ-related, albeit still potentially life threatening. Until more data on the disease in infancy become available, it is not possible to predict whether the sudden death syndrome in infants with sickle cell anemia is a common or a rare event. In the meantime, the diagnosis must be considered in cases of acute general illness and unexplained death, especially in ethnic groups where the sickle cell gene is known to occur commonly.
Prevention of some of the sequelae of sickle cell diseases can be achieved by newborn screening (see “Diagnosis,” above). Another form of prevention is based on prenatal diagnosis. Parents can be screened for the carrier state, and if they are carriers they can be provided with genetic counseling and educated about the options of not having children or of having pregnancies monitored for the occurrence of a sickle cell disease in the fetus. Since approximately half of the children with sickle cell diseases have only one parent with sickle hemoglobin, effective screening programs must do more than merely detect the presence of this abnormal hemoglobin. They must also use means that will permit detection of hemoglobin C and of b-thalassemia trait. Because of the benign clinical nature of b-thalassemia, hemoglobin C, and sickle cell traits, no useful purpose other than that of genetic counseling seems to be served by screening populations for these carrier states. Indeed, misunderstanding concerning the significance of the carrier states has led to unwarranted harm to individuals who are detected as carriers in screening programs.387
Many screening programs have been implemented and the number and background of participants have been described.388,389 and 390 However, only scant data permitting assessment of the actual effect of screening programs on birth frequency of infants with sickle cell disorders are available. In Guadeloupe 62 percent of the group of mothers at risk for bearing children with sickle disease underwent prenatal diagnosis, which allowed identification of 27 SS fetuses, with an induced abortion rate of 70 percent. Such data are, of course, highly culture dependent, and very different results might be obtained elsewhere.
Sickle cell trait is the heterozygous state for the sickle cell diseases and is the most benign form of the sickling disorders.
The properties of sickle hemoglobin have been described above. In sickle cell trait less than one-half of the hemoglobin in each red cell is hemoglobin S. The abundance of normal hemoglobin A in the cell prevents sickling under most physiologic circumstances; sickle cell trait cells will sickle at an oxygen tension of about 15 torr.79
Sickle cell trait is inherited as an autosomal dominant disorder. It affects some 8 percent of African Americans and an even higher percentage of the population in Africa (see “Inheritance,” above). Interaction between a-thalassemia and sickle cell trait to modify the amount of sickle hemoglobin has been described above.
Sickle cell trait does not produce any abnormalities of the blood counts and is an exceedingly rare cause of morbidity. Red cell life span is normal in normoxic persons with sickle cell trait.391 Not only patients but even physicians392 often appear to believe that sickle cell trait represents a mild type of sickle cell disease. Cerebral thrombosis, mishaps during anesthesia, and sudden death attract little notice when occurring in a person who does not have a known genetic variant, but the same occurrence in the 1 of 12 African Americans who have this trait immediately raises the question of a cause-and-effect relationship. Thus, there is a legion of anecdotal reports suggesting that sickle cell trait contributed to a patient’s illness.187,188,393,394,395 and 396 There may, however, be certain situations in which a risk is plausible. Thus, in severe cyanotic congenital heart diseases, such as tetralogy of Fallot, patients with sickle cell trait may show signs of hemolysis.397 In reality, the morbidity and possible mortality associated with sickle cell trait is very low and therefore difficult to document accurately. It seems to be limited largely to renal lesions (see Fig. 47-6) leading to hematuria that is otherwise unexplained and possibly to thromboembolic episodes involving the lung. In a massive study encompassing over 65,000 consecutively admitted African American male patients in 13 U.S. Veterans Administration hospitals,73 slightly higher incidences only of hematuria of unspecified cause (2.5 percent versus 1.3 percent) and pulmonary embolism (2.2 percent versus 1.5 percent) were found. No age stratification was found, indicating that the life span of patients with sickle cell trait is normal. Surgical patients with sickle cell trait had no greater perioperative mortality, no longer postoperative stay, and no greater mortality than those with normal hemoglobin. Similar conclusions have been drawn in other studies.398 It has not been possible to document any differences from normal in cardiovascular function of sickle cell trait subjects even when they were subjected to maximum exercise399,400,401,402 and 403; indeed, persons with sickle trait were overrepresented among champion athletes in the Ivory Coast.404
Sudden death resulting from rhabdomyolysis has been reported anecdotally in numerous subjects with sickle cell trait following severe exercise.396,405,406,407,408 and 409 An extensive investigation of episodes of sudden death showed a statistically significant excess in the number of patients with sickle cell trait.410 It is believed that the hyposthenuria (see “Other Clinical Manifestations, Genitourinary System,” above) in combination with heat and extreme stress may trigger this catastrophic and usually fatal event.
Because of reports of splenic infarction in individuals thought to have sickle cell trait who were flying in unpressurized aircraft411,412 or who ascended to very high altitudes,413 there has been concern about the safety of permitting persons with sickle cell trait to fly. Since commercial aircraft maintain a cabin pressure equivalent to that encountered at 5000 to 7000 feet (1500 to 2100 m), this concern is unwarranted.81 It appears that when splenic infarction does occur at high altitudes, non-African persons with sickle trait are much more likely to be affected than are Africans.80
The diagnosis of sickle cell trait depends upon demonstration of the presence of hemoglobin S and hemoglobin A in the affected individual. The amount of hemoglobin S is always less than the concentration of hemoglobin A. In contrast, in sickle cell b+-thalassemia the amount of hemoglobin S exceeds that of hemoglobin A.
Because of its benign features, sickle cell trait does not require treatment and does not appear to affect life span.73
Hemoglobin C was the second abnormal hemoglobin to be described, not long after the description of hemoglobin S.414 The homozygous state (CC disease) was described independently by Spaet et al415 and by Ranney et al416 in 1953. Hemoglobin C trait is the heterozygous state in which hemoglobin C is inherited together with normal hemoglobin. The combination with sickle cell hemoglobin, SC disease, has been described in the discussion of sickle cell anemia, under “The Sickle Cell Diseases,” above.
In hemoglobin C, glutamic acid in the sixth position from the N terminal of the b chain has been replaced by lysine.417 Red cells containing principally hemoglobin C are more rigid than normal,418 and their fragmentation in the circulation may result in the formation of microspherocytes. Intraerythrocytic crystals of oxygenated Hb C are found in the red cells, especially in splenectomized patients,418,419 and the formation of crystals is inhibited by hemoglobin F.420 The red cell life span is shortened to a mean of 30 to 35 days.421 The rate of hemoglobin production in hemoglobin C disease has been reported to be 2.5 to 3 times normal.422 Erythrocytes from patients with hemoglobin C disease have a low oxygen affinity, possibly due to a reduction for unknown reasons of the intracellular pH.423 This may contribute to the mild anemia that is usually present.
Hemoglobin C is found in 17 to 28 percent of West Africans, particularly east of the Niger River in the vicinity of North Ghana.424,425 The selective factors that account for this high prevalence are unknown at present. The prevalence among African Americans is 2 to 3 percent.73,426 Sporadic cases also have been reported in other populations, including Italians427 and Afrikaners.101
Splenomegaly is a fairly constant feature of hemoglobin C disease and may be associated with fleeting abdominal pain. However, there is little evidence for clinically significant hemodynamic disturbances.428 Women with hemoglobin C disease appear to tolerate pregnancy well.429 Children have mild anemia with few symptoms and normal growth.430
In hemoglobin C disease the hemoglobin level ranges from 8 to 12 g/dl. There is a marked increase in the number of target cells in the blood film (see Fig. 47-9). Some target cells are also present in the trait. Occasionally, intraerythrocytic hemoglobin crystals may be seen on the blood film, and these may appear in larger numbers if the red cells have been dehydrated either by drying or by suspension in a hypertonic solution (see Chap. 22). The osmotic fragility of the red cells may be decreased.
The diagnosis of homozygous hemoglobin C disease is achieved by electrophoresis, hemoglobin C moving to the same position as hemoglobin A2, hemoglobin E, and hemoglobin OArab at an alkaline pH. Hemoglobin C is readily distinguished from other hemoglobins by acid agar gel electrophoresis.
No specific therapy is available or required for patients with hemoglobin C disease. Anemia may become more severe following infections, but the overall prognosis is considered to be excellent.
In his early studies of the hemoglobinopathies, Itano431 encountered a white family with an abnormal hemoglobin that migrated at the same rate as hemoglobin S but did not sickle. Its solubility in the reduced state resembled that of hemoglobin A, and this new abnormal hemoglobin was designated hemoglobin D. Subsequently, this name was given to any hemoglobin variant that manifested the same electrophoretic properties as hemoglobin S at an alkaline pH but had normal solubility properties.
With the exact chemical analysis of hemoglobin variants, it became apparent that hemoglobin DLos Angeles was identical to hemoglobin DPunjab, both manifesting a substitution of glutamate for lysine at the 121st position in the b chain. Another “D” hemoglobin, GPhiladelphia, is, on the other hand, an a chain variant, with a substitution of asparagine for lysine at the sixty-eighth position.
Like the other structural mutations of hemoglobin, hemoglobin D trait is the heterozygous state for hemoglobin D and hemoglobin A, while the homozygous state for hemoglobin D is designated hemoglobin D disease. Hemoglobin DPunjab is found in frequencies of approximately 3 percent in Northwest India.
The heterozygous state for hemoglobin D is entirely asymptomatic.432 The abnormal hemoglobin constitutes between 35 and 50 percent of the total hemoglobin. Homozygous hemoglobin D disease is very rare, and some patients originally believed to be homozygous for hemoglobin D433 subsequently were found to be heterozygous for hemoglobin D and b-thalassemia. A small number of true homozygotes have been described, however, and the clinical consequences are very mild.434
Hemoglobin E is so prevalent that it may be the most common abnormal hemoglobin,435 or second in prevalence only to hemoglobin S. It was first described in 1954, independently by Itano et al436 and by Chernoff et al.437
Hemoglobin E is the result of a b chain mutation, a2b226Glu®Lys.438 The amino acid substitution not only produces a hemoglobin that is somewhat unstable when subjected to oxidative stress,439 perhaps because of weakening of the bonds between the monomers constituting the hemoglobin tetramer, but the nucleotide substitution also creates a new potential splicing sequence, so that some of the messenger may be spliced improperly.440 The formation of unstable messenger accounts for the thalassemia-like nature of hemoglobin E trait and disease.
The inheritance of hemoglobin E is the same as that of the other b chain mutants. Heterozygotes for hemoglobin E and hemoglobin A have hemoglobin E trait, while homozygotes for hemoglobin E are designated as having hemoglobin E disease. Hemoglobin E, like hemoglobin S and hemoglobin C, occurs with sufficient frequency to be considered a polymorphism. The distribution of the gene for this b chain mutation is illustrated in Fig. 47-10. Decreased falciparum malaria parasitemia has been documented in patients with hemoglobin E trait,441 and resistance to malaria may be the advantage that has led to high gene frequencies.

FIGURE 47-10 Distribution of hemoglobin E in Southeast Asia. Gene frequencies: cross-hatching indicates >0.2 percent; narrow hatching indicates 0.1 to 0.2 percent; wide hatching indicates 0.02 to 0.1 percent; dotted area indicates <0.02 percent and sporadic occurrence. (Flatz,442 by permission.)

Hemoglobin E is found principally in Burma, Thailand, Laos, Cambodia, Malaysia, and Indonesia, and in some areas it occurs with a carrier rate of 30 percent.442 On the other hand, it is not prevalent among the Chinese. Studies of restriction length polymorphisms in the b-globin cluster indicate that the hemoglobin E mutation has arisen several times independently.443
Although the prevalence of the gene for hemoglobin E is quite high in Southeast Asia (see Fig. 47-10), relatively few patients with homozygous E disease, as distinguished from hemoglobin E b-thalassemia, have been described.444,445 When homozygous E disease is encountered, it is associated with marked microcytosis and hypochromia but little or no anemia. Splenomegaly is unusual, and the red cell life span is normal. Clinically, the state closely resembles b-thalassemia minor.
In the hemoglobin E carrier state 30 to 45 percent of the hemoglobin is hemoglobin E,437 and such carriers are asymptomatic but do manifest microcytosis.446
The clinical manifestations of the heterozygous state between hemoglobin E and b-thalassemia are quite variable in severity447 and resemble those of homozygous hemoglobin E disease, with moderate anemia and splenomegaly representing the usual manifestation.
Hemoglobin E is electrophoretically slow in an alkaline medium, comigrating with hemoglobin C and A2. The characteristic blood change is microcytosis—mild in the trait and more severe in the homozygous state and in hemoglobin E b-thalassemia. There is a modest decrease in the a-/non-a-globin chain synthetic ratio445 and a minimal decrease in whole blood oxygen affinity.437,444
The prognosis seems to be good, although no thorough studies of the natural history of the disease have been carried out. Splenectomy increases the red cell life span and ameliorates anemia in hemoglobin E b-thalassemia,448,449 but its role in homozygous hemoglobin E disease has not been delineated. In one family manifesting both pyrimidine 5′-nucleotidase deficiency and homozygous hemoglobin E disease, those with both defects had more severe anemia than those inheriting one alone.450
In comparison with hemoglobins S, C, D, and E, other abnormal hemoglobins are rare. Some, such as the unstable hemoglobins (see Chap. 48), the hemoglobins producing erythrocytosis (see Chap. 61), and those producing cyanosis (see Chap. 49), are of clinical importance. Many of the other hemoglobins do not produce significant clinical alterations but have nonetheless been important in clarifying the role of individual amino acids in the structure and function of the hemoglobin molecule. Some of the more common hemoglobin variants are summarized in Table 47-1. Complete compendia of mutations affecting hemoglobin have been published,451 and further sources may be found at http://globin.cse.psu.edu/.



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Ernest Beutler, Marshall A. Lichtman, Barry S. Coller, Thomas J. Kipps, and Uri Seligsohn
Williams Hematology