Hiding in Plain Sight: C3 Glomerulonephritis (C3GN) Diagnosed in a Living Kidney Donor

Introduction: Despite advancements in diagnostic capabilities, genetic testing and access to nephrology care, the underlying cause of End Stage Kidney Disease (ESKD) is still unknown in many patients. We present a case of C3 glomerulonephritis diagnosed 10 years after kidney donation to a family member. Case Description: A 36-year-old Caucasian male was referred for evaluation of persistent hematuria. Ten years prior he was a living kidney donor for his father. His creatinine was 1.29 mg/dl and urinalysis was significant for 1+ blood without proteinuria. The urologic evaluation was unremarkable. Family history is pertinent for ESKD in his father that was attributed to glomerulonephritis, but kidney biopsy was never performed. The serologic work up for hematuria was negative. Genetic testing was pursued and was significant for a pathogenic variant in CFH (associated with susceptibility to aHUS and C3G). Functional testing was negative for anti-CFH antibody but his soluble C5b-9 was elevated. Genetic testing was done on his father which was significant for the same mutations He underwent kidney biopsy for further evaluation that showed C3 dominant immune complex deposition in the glomeruli on IF and EM. There was no mesangial or endocapillary hypercellularity by light microscopy. The findings were indicative of C3 glomerulonephritis. Discussion: This case illustrates the importance of evaluation of causes of ESKD in all patients, particularly when being evaluated for living related kidney donation. In this case, the patient’s fathers ESKD was unknown and ultimately attributed to a hereditary complement mediated disease. If known prior to donation, it is unlikely the patient would have qualified as a donor. Although C3GN is a rare complement mediated disease there are now therapeutic options that can be utilized in both de novo and recurrent cases.