Hemolytic uremic syndrome (HUS) is defined by a
triad of microangiopathic hemolytic anemia (characterized
by schistocytes and helmet cells, as shown in
Fig. 1), thrombocytopenia, and renal dysfunction. It is
a leading cause of acquired renal failure in children
in the US. In almost all diagnosed HUS cases there is
a preceding diarrheal illness, which defines typical
HUS. The most common pathogens causing HUS
are Escherichia coli (specifically toxin-producing
O157:H7, along with other E. coli strains), followed
by Shigella, and finally, a variety of other less common
bacterial causes. If the disease is not preceded
by a diarrheal prodrome, then it is considered atypical
HUS.
HUS presents most commonly in young schoolaged
children. In typical HUS, the onset of complications
occurs 3–7 days (but can be up to 14 days) after
the onset of the symptoms of gastroenteritis. These intestinal
symptoms may be severe enough to cause hospitalization
secondary to dehydration or self-limiting
with only mild symptoms. Oliguria due to renal damage
can be missed early in the illness because it may be
thought to be associated with dehydration from the
ongoing diarrheal losses or poor oral intake.
Microangiopathic hemolytic anemia is one of the
key features that define HUS. It is characterized by a
negative Coombs test despite ongoing hemolysis, and
hemoglobin values are generally 8 g/dL. The periph-