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Hemolytic Uremic Syndrome, Post-diarrheal (HUS)
1996 Case Definition
Clinical description
Hemolytic uremic syndrome (HUS) is characterized by the
acute onset of microangiopathic hemolytic anemia, renal injury, and low
platelet count. Thrombotic thrombocytopenic purpura (TTP) also is characterized
by these features but can include central nervous system (CNS) involvement
and fever and may have a more gradual onset. Most cases of HUS (but few
cases of TTP) occur after an acute gastrointestinal illness (usually
diarrheal).
Laboratory criteria for diagnosis
The following are both present at some time during the
illness:
- Anemia (acute onset) with microangiopathic changes
(i.e., schistocytes, burr cells, or helmet cells) on peripheral
blood smear and
- Renal injury (acute onset) evidenced by either hematuria,
proteinuria, or elevated creatinine level (i.e., greater than or
equal to 1.0 mg/dL in a child aged less than 13 years or greater
than or equal to 1.5 mg/dL in a person aged greater than or equal
to 13 years, or greater than or equal to 50% increase over baseline)
Note: 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 less than 150,000/mm3, other diagnoses
should be considered.
Case classification
Probable:
- An acute illness diagnosed as HUS or TTP that meets
the laboratory criteria in a patient who does not have a clear
history of acute or bloody diarrhea in preceding 3 weeks or
- An acute illness diagnosed as HUS or TTP, that a)
has onset within 3 weeks after onset of an acute or bloody diarrhea
and b) meets the laboratory criteria except that microangiopathic
changes are not confirmed
Confirmed: an acute illness diagnosed as HUS
or TTP that both meets the laboratory criteria and began within 3 weeks
after onset of an episode of acute or bloody diarrhea
Comment
Some investigators consider HUS and TTP to be part of
a continuum of disease. Therefore, criteria for diagnosing TTP on the
basis of CNS involvement and fever are not provided because cases diagnosed
clinically as postdiarrheal TTP also should meet the criteria for HUS.
These cases are reported as postdiarrheal HUS. Most diarrhea-associated HUS is
caused by Shiga toxin-producing Escherichia coli, most commonly E. coli O157.
If a patient meets the case definition for both Shiga toxin-producing E. coli
(STEC) and HUS, the case should be reported for each of the conditions.
See also:
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