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, 50 ×.) Shown are multiple schistocytes (fractured red blood cells), pathognomonic of microangiopathic hemolytic disorders such as hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura. This is a hemolytic state, as evidenced by an increased reticulocyte count and very often the presence of polychromasia (immature, slightly blue erythrocytes). Very few platelets are present. (Used, with permission, from L Damon.)
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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