Which of the following disorders characteristically shows a depressed serum C3 level with a NORMAL C4 level?

• A Post-streptococcal glomerulonephritis ✓
• B Systemic lupus erythematosus nephritis
• C Mixed cryoglobulinemic glomerulonephritis associated with hepatitis C
• D Severe hereditary angioedema

Explanation

Post-streptococcal glomerulonephritis activates the alternative and lectin pathways, so C3 falls while C4, consumed only by classical pathway activation, remains normal. Lupus and mixed cryoglobulinemia activate the classical pathway through immune complexes, lowering both C3 and C4. Hereditary angioedema reflects C1 inhibitor deficiency with low C4 but normal C3, making it the mirror image and the strongest distractor here.

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.