Fragmentation Hemolysis (See Table 451-1)

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