A 5-year-old child develops the sudden onset of bloody diarrhea, vomiting of blood, hematuria, and renal failure following a flulike gastrointestinal illness. The blood urea nitrogen (BUN) level is markedly increased, but fibrin degradation products and blood clotting times are within normal limits. A peripheral blood smear reveals poikilocytes, schistocytes, and a decrease in the number of platelets. No fever or neurologic symptoms are present. What is the best diagnosis for this patient?

Hemolytic-uremic syndrome (HUS) is similar to thrombotic thrombocytopenic purpura (TTP) in that it produces a microangiopathic hemolytic anemia, but it is distinguished from TTP by the lack of neurologic symptoms and by the severe acute renal failure, which is manifested clinically by a markedly increased serum BUN. Classic HUS is seen in children and is related to infection, usually acquired from contaminated ground meat, by verocytotoxin-producing Escherichia coli. This toxin is similar to Shigella toxins, which, together with E. coli and viruses, are causes of the adult form of HUS. Multiple microthrombi in glomerular capillaries result in renal failure, while systemically the microthrombi cause microangiopathic hemolytic anemia. Subsequently thrombocytopenia develops and leads to a bleeding diathesis, seen as vomiting of blood and hematuria. Disseminated intravascular coagulopathy (DIC) is separated from these two thrombotic microangiopathic syndromes by its excessive activation of the clotting system, which results in increased fibrin degradation products (FDP or FSP) and prolonged clotting times (PT and PTT) due to depletion of coagulation factors. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.