Atypical Hemolytic–Uremic Syndrome

The hemolytic–uremic syndrome, which is characterized by nonimmune hemolytic anemia, thrombocytopenia, and renal impairment, occurs most frequently in young children. Most cases are secondary to infection with Escherichia coli O157:H7 and other Shiga-toxin–producing strains. However, approximately 10% of cases are atypical and not associated with infection. This article reviews current concepts about the pathobiology of atypical hemolytic–uremic syndrome and its diagnosis and management.