Thrombotic thrombocytopenic purpura without schistocytes on the peripheral blood smear

A hallmark of the clinical syndrome of thrombotic thrombocytopenic purpura (TTP) is evidence of microangiopathic hemolytic anemia. The presence of schistocytes on the peripheral blood smear, elevated plasma lactic dehydrogenase, and decreased haptoglobin concentration are used as evidence of microangiopathic hemolytic anemia to make a diagnosis of TTP. This report describes a case of recurrence of TTP in the absence of schistocytes in the peripheral blood smear during the recurrent episode. Although careful attention should be paid to microscopic examination of a blood smear in any patient presenting with acute renal failure and thrombocytopenia, this case emphasizes the need to consider TTP-hemolytic uremic syndrome in the differential diagnosis, even in the absence of peripheral schistocytosis.