A 35-year-old woman presents with a 2-week history of haematuria, proteinuria (2.8 g/day), periorbital oedema, and oliguria. Blood pressure is 165/100 mmHg. Serum complement C3 is markedly reduced; C4 is normal. ANCA and anti-GBM are negative. Throat swab 3 weeks prior grew Streptococcus pyogenes. The most likely diagnosis is:

• A IgA nephropathy (Berger's disease)
• B Membranoproliferative glomerulonephritis type I
• C Post-streptococcal glomerulonephritis (PSGN) ✓
• D Lupus nephritis class III

Explanation

Post-streptococcal GN classically presents 1–3 weeks after a throat (or 3–6 weeks after skin) streptococcal infection with nephritic syndrome: haematuria, proteinuria, hypertension, oliguria, and oedema. Selective reduction in C3 with normal C4 indicates activation of the alternative complement pathway — the hallmark serological finding of PSGN. IgA nephropathy presents with synpharyngitic haematuria (concurrent with URTI). MPGN reduces both C3 and C4.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.