Causes mild to severe Coombs positive hemolytic anemia Hemolytic-uremic syndrome (H.U.S.) is the most common cause of acute renal failure in young children. It is classically characterized by the triad of - Microangiopathic hemolytic anemia - Thrombocytopenia - Uremia Etiology Hemolytic uremic syndrome is preceeded by bacterial infections The bacterias commonly associated are : E.coli (Verocytogenic E.coli is the most common ause of hemolytic uremic syndrome) in Nelson states "An acute enteritis with diarrhoae caused by shiga-like toxin producing escherichia coli (verocytogenic E. coli) 0157:117 precedes 80% or more of HUS cases in developed countries" An impoant point Some say that option 'a' was - "Not commonly caused by verocytogenic E.coli in Asia" If this was the option then it is a true statement. - The infection associated with H. U.S. varies with region In developed countires (Noh America and Europe) - Verocytogenic E coli or Shiga like toxin producing Eschererichia coli is the most common cause (80% of all the cases). In Asia (India) - Shigella dysenteriae is the chief pathogen. The anemia associated with hemolytic uremic syndrome is coomb's negative hemolytic anemia. Coomb's positive hemolytic anemia occurs when the anemia is caused due to autoantibodies produced in the body. In H.U.S. the hemolytic anemia is caused by mechanical damage to R.B.C. when they pass through nucrothrombi (which are formed in capillaries due to platelet aggregation). The red cells while passing through these capillaries get attached to the thrombus and gets fragmented causing hemolysis, Autoantibodies have nothing to do with hemolytic uremic syndrome. So the anemia will not be coomb's positive. Thrombocytopenia in H.U.S. A low platelet count can usually but not always be detected early in the illness, but it may then become normal or even high. If a platelet count obtained within 7 days after onset of the acute gastrointestinal illness is not <150,000/mm3, other diagnosis should be considered. Recurrence in H.U.S. Recurrence is rare in H.U.S. There may be disease recurrence only in familial or non diarrhoea associated cases.