Hemolytic-uremic syndrome without evidence of microangiopathic hemolytic anemia on peripheral blood smear

We report the case of an 18-year old man with hemolytic-uremic syndrome (HUS) having a classic clinical presentation and diagnostic renal pathology without evidence of microangiopathic hemolytic anemia (MAHA) by peripheral blood smear. Indirect evidence of hemolysis was suggested by mild anemia, elevation of serum lactate dehydrogenase, and examination of the patient's bone marrow. We postulate that in this case the inability to detect schistocytes in the peripheral smear reflected a low degree of hemolysis. Review of the literature revealed that evidence of fragmented erythrocytes by peripheral smear is not always present in HUS, yet this observation has received little attention. Thus, the diagnosis of HUS need not include overt evidence of MAHA as is traditionally taught.