Case Report: COVID-19 unmasks factor H mutation-driven hemolytic uremic syndrome in a previously undiagnosed septuagenarian kidney transplant recipient.

Thrombotic microangiopathy (TMA) after kidney transplantation presents a significant diagnostic and therapeutic challenge. Complement-mediated thrombotic microangiopathy (CM-TMA), caused by dysregulation of the alternative complement pathway, is frequently associated with predisposing variants in complement-regulatory genes but typically requires additional triggers for clinical manifestation. Ravulizumab, a long-acting terminal complement inhibitor, has demonstrated efficacy in native kidney disease, but data in transplant recipients remain limited. We present a 75-year-old kidney transplant recipient in whom previously unrecognized CM-TMA was triggered by COVID-19 infection and successfully treated with ravulizumab. This case underscores the importance of considering CM-TMA in the differential diagnosis of posttransplant TMA and in patients with end-stage kidney disease of uncertain origin, demonstrating that age alone should not preclude diagnostic consideration, and supports ravulizumab as an effective therapeutic option in this setting.