Abstract
The complement system plays a crucial role in innate immunity and inflammation regulation, with component C3 being central to its activation. Isolated C3 deficiency is rare and may occur secondary to immune, infectious, or inflammatory conditions. We present a 23-year-old woman admitted with nausea, vomiting, and right lower abdominal pain. Laboratory tests revealed acute kidney injury (creatinine: 1.71 mg/dL; urea: 64 mg/dL), and imaging identified a hemorrhagic ovarian cyst rupture with free peritoneal fluid. Complement testing revealed low serum C3 levels with normal C4 and negative autoimmune and infectious markers. The patient was treated conservatively with hydration, and renal function returned to normal within days. This case highlights a rare association between hemorrhagic ovarian cyst rupture and acute kidney injury in the context of isolated C3 deficiency. Although no underlying systemic disease was detected, the transient complement activation may reflect an acute inflammatory response. Isolated complement abnormalities should be interpreted with clinical context and followed closely.