Definition
Haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy defined by a triad:
- Microangiopathic haemolytic anaemia (MAHA) — with schistocytes
- Thrombocytopenia
- Acute kidney injury
Typical (STEC) HUS
- Follows infection with Shiga-toxin-producing E. coli (classically O157:H7), often after a prodrome of bloody diarrhoea
- Mainly affects children
- Management is supportive (fluids, transfusion, dialysis if needed); antibiotics are generally avoided (may increase toxin release)
Atypical HUS
- Due to dysregulation of the alternative complement pathway (genetic or acquired)
- No diarrhoeal prodrome; may relapse
- Treated with the complement C5 inhibitor eculizumab
Investigations
- Blood film: schistocytes, low platelets
- Haemolysis markers: raised LDH, low haptoglobin, raised bilirubin, negative direct antiglobulin (Coombs) test
- Normal coagulation (distinguishes from DIC)
- Stool culture/Shiga-toxin testing; complement studies for atypical disease
HUS vs TTP
Both are thrombotic microangiopathies. TTP features prominent neurological signs and fever and is caused by ADAMTS13 deficiency; renal involvement dominates in HUS.
MRCP-specific traps
- HUS after bloody diarrhoea in a child = STEC; avoid antibiotics, manage supportively.
- Normal clotting with thrombocytopenia and haemolysis points to a microangiopathy (HUS/TTP), not DIC.
- Relapsing HUS without diarrhoea suggests atypical (complement-mediated) disease → eculizumab.
Summary
HUS is a thrombotic microangiopathy — MAHA (schistocytes), thrombocytopenia and AKI, with normal clotting. Typical STEC-HUS follows bloody diarrhoea in children and is managed supportively (avoid antibiotics); atypical, complement-mediated HUS is treated with eculizumab. Distinguish from TTP (neurology, ADAMTS13).
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