Atypical hemolytic uremic syndrome (aHUS) is rare and comprises the triad of 
microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. 
Recently, abnormalities in the mechanisms underlying complement regulation have 
been focused upon as causes of aHUS. The prognosis for patients who present with 
aHUS is very poor, with the first aHUS attack being associated with a mortality 
rate of approximately 25%, and with approximately 50% of cases resulting in 
end-stage renal disease requiring dialysis. If treatment is delayed, there is a 
high risk of this syndrome progressing to renal failure. Therefore, we have 
developed diagnostic criteria for aHUS to enable its early diagnosis and to 
facilitate the timely initiation of appropriate treatment. We hope these 
diagnostic criteria will be disseminated to as many clinicians as possible and 
that they will be used widely.