Chapter 459 Hemolytic Anemias Secondary to Other Extracellular Factors
Red blood cell (RBC) destruction may occur in hemolytic anemias because of mechanical injury as the cells traverse a damaged vascular bed. Damage may be microvascular when RBCs are sheared by fibrin in the capillaries during intravascular coagulation or when renovascular disease accompanies the hemolytic-uremic syndrome (Chapter 512) or thrombotic thrombocytopenic purpura (Chapter 478.5). Larger vessels may be involved in Kasabach-Merritt syndrome (giant hemangioma and thrombocytopenia; Chapter 499) or when a replacement heart valve is poorly epithelialized. The blood film shows many “schistocytes,” or fragmented cells, as well as polychromatophilia, reflecting the reticulocytosis (see Fig. 452-4F). Secondary iron deficiency may complicate the intravascular hemolysis because of urinary hemoglobin and hemosiderin iron loss (see Fig. 451-2). Treatment should be directed toward the underlying condition, and the prognosis depends on the effectiveness of this treatment. The benefit of transfusion is transient because the transfused cells are destroyed as quickly as those produced by the patient.
Extensive burns may directly damage the RBCs and cause hemolysis that results in the formation of spherocytes. Blood loss and marrow suppression may contribute to anemia and require blood transfusion. Erythropoietin (EPO) has been used as treatment for diminished RBC production.
The anemia of uremia is multifactorial in origin. EPO production may be decreased and the marrow suppressed by toxic metabolites. Furthermore, the RBC life span often is shortened owing to retention of metabolites and organic acidemia. The use of EPO in chronic renal disease has markedly decreased the need for blood transfusion.
A change in the ratio of cholesterol to phospholipids in the plasma may result in changes in the composition of the RBC membrane and shortening of the RBC life span. Some patients with liver disease have many target RBCs on the blood film, whereas others have a preponderance of spiculated cells. These morphologic changes reflect the alterations in the plasma lipid composition.
Bacterial sepsis due to Haemophilus influenzae, staphylococci, and streptococci may be complicated by accompanying hemolysis. Particularly severe hemolytic anemia has been observed in clostridial infections and results from a hemolytic clostridial toxin. Large numbers of spherocytes may be seen on the blood film. Spherocytic hemolysis also may be noted after bites by various snakes, including cobras, vipers, and rattlesnakes, which have phospholipases in their venom. Large numbers of bites by insects, such as bees, wasps, and yellow jackets, also may cause spherocytic hemolysis by a similar mechanism (Chapter 706).
An acute and self-limited episode of hemolytic anemia may precede by years the onset of hepatic or neurologic symptoms in Wilson disease. This event appears to result from the toxic effects of free copper on the RBC membrane. The blood film often (but not always) shows large numbers of spherocytes, and the Coombs test result is negative. Because early diagnosis of Wilson disease permits prophylactic treatment with penicillamine and prevention of hepatic and neurologic disease, correct assessment of this rare type of hemolysis is important.
Grudeva-Popova JG, Spasova MI, Chepileva KG, et al. Acute hemolytic anemia as an initial clinical manifestation of Wilson’s disease. Folia Med (Plovdiv). 2000;42:42-46.
Sakuri J, Nagahama M, Oda M. Clostridium perfringens alpha-toxin: characterization and mode of action. J Biochem (Tokyo). 2004;136:569-574.