A 7-year-old boy develops periorbital swelling, cola colored urine, and hypertension 10 days after impetigo. Urinalysis shows red cell casts and proteinuria of 1.5 g/day. Which complement profile is expected?

• A Normal C3 with low C4
• B Low C3 with low C4
• C Low C3 with normal C4 ✓
• D Normal C3 and normal C4

Explanation

Post streptococcal glomerulonephritis activates complement through the alternative and lectin pathways, producing a depressed A3 with a normal A4, a pattern typical of postinfectious glomerulonephritis, MPGN, and A3 glomerulopathy. Low A4 alongside low A3 points to classical pathway consumption, seen in lupus nephritis and mixed cryoglobulinemia. Recognizing this split helps distinguish infection related glomerulonephritis from immune complex disease driven by classical pathway activation.

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.