The microangiopathic hemolytic anemias are a group of disorders in which red blood cell fragmentation takes place. The anemia is intravascular, producing hemoglobinemia, hemoglobinuria and, in severe cases, methemalbuminemia. The hallmark of the disorder is the finding of fragmented red blood cells (schistocytes, helmet cells) on the peripheral blood smear (eFigure 13–17).
Hemolytic-uremic syndrome, peripheral blood smear. Characteristic findings include anisocytosis (red cells of varying size), spherocytosis (red cells that are sphere-shaped rather than biconcave disks), and poikilocytosis (red cells that are abnormally shaped) as well as an absence of platelets, reflecting a marked thrombocytopenia (low platelet level). The fragmented RBC with pointed ends are schistocytes, consistent with this being a microangiopathic process. (Reproduced, with permission, from Lichtman MA, Shafer MS, Felgar RE, Wang N. Lichtman's Atlas of Hematology. McGraw-Hill, 2016.)
These fragmentation syndromes can be caused by a variety of disorders (Table 13–8). Thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome are the most important of these and is discussed in Chapter 14. Clinical features are variable and depend on the underlying disorder. Thrombocytopenia is uniformly present. Coagulopathy is variably present and depends on the underlying disorder driving the microangiopathy.
Chronic microangiopathic hemolytic anemia (such as is present with a malfunctioning cardiac valve prosthesis) may cause iron deficiency anemia because of continuous low-grade hemoglobinuria.
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