Pregnancy aHUS Complement Low ADAMTS13 Normal — ESENeph MCQ

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HardPregnancy & RenalPregnancy aHUS Complement Low ADAMTS13 NormalESENeph

A 27-year-old woman at 28 weeks' gestation develops AKI with creatinine 280 umol/L, platelet count 42 x 10^9/L, LDH 1800 U/L, haptoglobin undetectable, and schistocytes on blood film. ADAMTS13 activity is 68% (normal >67%). Complement C3 is 0.55 g/L (low). What is the most likely diagnosis?

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Correct answer: C — Atypical haemolytic uraemic syndrome

This is a thrombotic microangiopathy (TMA) in pregnancy with microangiopathic haemolytic anaemia (schistocytes, elevated LDH, low haptoglobin), thrombocytopenia, and AKI. ADAMTS13 is normal (>67%), excluding TTP. Low complement C3 suggests complement-mediated TMA — atypical HUS (aHUS). Pregnancy is a well-recognised trigger for aHUS, particularly in the second/third trimester and postpartum. HELLP syndrome typically occurs with pre-eclampsia features (hypertension, proteinuria, liver involvement) and does not characteristically cause low complement. Management requires eculizumab (anti-C5 monoclonal antibody) and consideration of delivery timing.

Reference: KDIGO 2025 – Complement-Mediated Kidney Diseases; Fakhouri et al 2010 – Pregnancy-Associated aHUS