A 45-year-old woman presents with hemoptysis and rapidly rising creatinine. Urinalysis shows red blood cell casts. Chest imaging reveals multiple bilateral nodules, one of which has cavitated. Renal biopsy shows focal necrotizing glomerulonephritis with crescents. Which laboratory test is most likely positive?
- A c-ANCA directed against proteinase 3 ✓
- B Anti-glomerular basement membrane antibodies against type IV collagen
- C p-ANCA directed against myeloperoxidase
- D Anti-Ro (SS-A) antibodies
Correct answer: A. c-ANCA directed against proteinase 3
Explanation
Cavitating pulmonary nodules with pauci-immune crescentic glomerulonephritis are characteristic of granulomatosis with polyangiitis, which is strongly associated with c-ANCA targeting proteinase 3. Anti-GBM antibodies occur in Goodpasture syndrome, which produces diffuse alveolar hemorrhage rather than discrete cavitating granulomatous nodules, making it the key distractor. p-ANCA against myeloperoxidase is linked to microscopic polyangiitis and Churg-Strauss vasculitis.
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.