CASE PRESENTATION: A 20 year-old female with no significant past medical history presented with 3 days of cough and shortness of breath. She also endorsed 4 weeks of fatigue, decreased appetite, chest pain, and subjective fevers. She denied chills, night sweats, weight loss, travel, or pets. She was diagnosed with a viral syndrome on her first emergency department visit and discharged without testing. She returned 2 days later with the same complaints. Vital signs were BP 151/94, HR 110, RR 15, T 99, SpO2 85%. Significant physical examination findings were rhonchi with decreased breath sounds at the bases. She was intubated for respiratory failure and blood-tinged secretions were noted in the endotracheal tube. Laboratory studies showed creatinine 26.6 mg/dL, BUN 145 mg/dL, bicarbonate 13 mEq/L, hemoglobin 9.4 g/dL, and platelet count 103 k/uL. Chest radiography revealed multifocal airspace infiltrates. On bronchoscopy, serial BAL aliquots were gradually more hemorrhagic. ADAMTS13 activity was 44%. Renal biopsy revealed thrombotic microangiopathy. Genetic studies showed heterozygous abnormality of complement factor H (CFH). She was initiated on dialysis, high dose steroids, plasma exchange, and eculizumab. She was extubated on day 6 and discharged home with outpatient dialysis and weekly eculizumab injections.