A 9-year-old boy had acute nephritic syndrome after pharyngitis. Serum C3 was low during the acute episode. At six weeks of follow-up, repeat serum C3 is still markedly depressed and urinalysis shows continued hematuria. Which interpretation is most appropriate?

• A Expected course of post-streptococcal glomerulonephritis, continue observation
• B Low C3 indicates steroid resistant minimal change disease
• C Low C3 confirms conversion to anti-GBM disease
• D Persistent hypocomplementemia beyond 6 weeks suggests an alternate diagnosis such as membranoproliferative glomerulonephritis, and biopsy should be considered ✓

Explanation

In post-streptococcal glomerulonephritis, C3 typically returns to normal within about 6 to 8 weeks while urinary abnormalities can persist longer. Hypocomplementemia persisting beyond this window points to conditions with chronic alternative pathway activation, chiefly membranoproliferative glomerulonephritis and C3 glomerulopathy, warranting biopsy. Anti-GBM disease and minimal change disease are not complement consuming disorders, so neither explains a persistently low C3 level.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.