Post-infectious glomerulonephritis: Viva

Branch 1: Diagnosis and the streptococcal latency

The candidate should recognise that this girl has post-streptococcal glomerulonephritis and state the acute nephritic syndrome of haematuria, oedema, and hypertension. A strong candidate should emphasise the latency of two weeks between the sore throat and the haematuria as the key discriminator from IgA nephropathy, which produces haematuria during rather than after an infection. The candidate should link the low C3 with the normal C4 and the raised antistreptolysin O titre to confirm the diagnosis, and should state that the C3 is expected to recover within six to eight weeks. ^[1]

If the examiner asks about the differential, the candidate should distinguish PSGN from the other hypocomplementaemic glomerulonephritides. IgA nephropathy has a normal C3 and synpharyngic haematuria. Lupus nephritis lowers both C3 and C4, so a low C4 mandates an autoimmune screen. C3 glomerulopathy and membranoproliferative glomerulonephritis produce persistently low C3 that does not recover by eight weeks. The candidate should name the streptococcal antigens: the nephritis-associated plasmin receptor and streptococcal pyrogenic exotoxin B. ^[1]