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The microangiopathic hemolytic anemias (also referred to as “thrombotic microangiopathies”) are a group of disorders in which RBC 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 RBCs (schistocytes, helmet cells) on the peripheral blood smear (eFigure 15–17).

eFigure 15–17.

Hemolytic-uremic syndrome, peripheral blood smear. Characteristic findings include anisocytosis (RBCs of varying size), spherocytosis (RBCs that are sphere-shaped rather than biconcave disks), and poikilocytosis (RBCs that are abnormally shaped) as well as an absence of platelets, reflecting a marked thrombocytopenia (low platelet level). The fragmented RBCs 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 15–8), including infections, rheumatic conditions, pregnancy, inherited complement pathway gene mutations, and advanced adenocarcinomas. Idiopathic thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome are the most important of these and are discussed in Part 16. Clinical features are variable and depend on the underlying disorder. Thrombocytopenia is present in most but not all thrombotic microangiopathies. 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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