A 25-year-old man presents with rapidly progressive glomerulonephritis (RPGN). Renal biopsy shows circumferential crescents in >50% of glomeruli with parietal cell proliferation and fibrin. Direct immunofluorescence is negative (pauci-immune). What is the MOST likely serological finding?

• A Positive anti-GBM antibody (linear IgG on immunofluorescence)
• B Elevated ANA and anti-dsDNA (immune complex deposition)
• C Elevated serum C3 with low C4 (alternative pathway activation)
• D Positive ANCA (either c-ANCA/anti-PR3 or p-ANCA/anti-MPO) ✓

Explanation

Pauci-immune crescentic glomerulonephritis is characterized by the absence or scarcity of immune deposits on immunofluorescence ('pauci-immune'), distinguishing it from anti-GBM disease (linear IgG) and immune complex disease (granular deposits). Pauci-immune RPGN is associated with ANCA-associated vasculitides: c-ANCA/PR3 in granulomatosis with polyangiitis (Wegener's), and p-ANCA/MPO in microscopic polyangiitis and eosinophilic granulomatosis. ANCA is positive in >90% of cases.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.