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C3 Glomerulopathy — RACP Adult Medicine MCQ

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HardNephrologyC3 GlomerulopathyRACP Adult Medicine

A 30-year-old man presents with proteinuria (3.5 g/day), haematuria, and hypertension. Serum C3 is markedly low with normal C4. Renal biopsy shows a membranoproliferative pattern with electron-dense deposits along the glomerular basement membrane. What is the most likely diagnosis?

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Correct answer: D — C3 glomerulopathy (dense deposit disease)

Explanation lettering: E = shown as A · D = shown as B · B = shown as C · A = shown as D · C = shown as E

Membranoproliferative GN with markedly low C3, normal C4, and electron-dense deposits along the GBM is characteristic of C3 glomerulopathy (including dense deposit disease). It is caused by dysregulation of the alternative complement pathway. C4 is typically normal (unlike lupus nephritis where both C3 and C4 are low). Complement factor testing (factor H, I, B, and C3 nephritic factor) should be performed. Treatment is challenging and may include eculizumab for refractory disease.

Reference: eTG – 2025 – Nephrology; KDIGO – 2021 – Glomerular Diseases Guidelines