Salvaging sepsis-associated atypical hemolytic uremic syndrome with terminal complement blockade: A case report

Sepsis can trigger life-threatening atypical hemolytic uremic syndrome (aHUS) through dysregulated complement activation. Diagnosis is challenging due to overlapping features with septic shock, often leading to delayed recognition and high mortality.

A 23-year-old female with chronic kidney disease presented with a 3-day history of productive cough, fever, and progressive dyspnea, which rapidly escalated to respiratory failure, anuria, and coma within 24 hours.

Laboratory findings confirmed thrombotic microangiopathy (hemoglobin 57 g/L, platelets 69 × 109/L, schistocytes 0.3%, lactate dehydrogenase [LDH] 469 U/L) and acute kidney injury (creatinine 535 µmol/L). The diagnosis of complement-mediated aHUS was established by markedly elevated soluble C5b-9 (sC5b-9) (578 ng/mL) with preserved a disintegrin and metalloproteinase with thrombospondin motifs 13 activity (89%).

Critical care included mechanical ventilation and continuous renal replacement therapy. Specific aHUS therapy comprised plasma exchange (10 sessions) and complement blockade with eculizumab (900 mg weekly for 4 weeks, then 1200 mg every 2 weeks), accompanied by meningococcal prophylaxis.

By day 31, hematologic and renal parameters improved (platelets 72 × 109/L, LDH 273 U/L, creatinine 151 µmol/L). By day 51, complement activity normalized (sC5b-9 261 ng/mL, a 54.8% reduction), with full hematologic recovery (platelets 198 × 109/L, LDH 171 U/L), renal function near baseline (creatinine 96 µmol/L), and resolution of hemolysis.

In sepsis with persistent thrombocytopenia despite infection control, urgent sC5b-9 testing is critical to diagnose aHUS. Eculizumab, combined with supportive continuous renal replacement therapy and plasma exchange, can effectively reverse multi-organ failure even during active bacteremia, with serial sC5b-9 monitoring serving as a key biomarker for guiding therapy.