A 28-year-old man complains of nasal obstruction, bloody nose, cough, and bloody sputum. A chest X-ray displays cavitated lesions and multiple nodules within both lung fields. Urinalysis reveals 3+ hematuria and red blood cell casts. Laboratory studies show anemia and elevated serum levels of C-ANCA (antineutrophil cytoplasmic antibody). Peripheral eosinophils are not increased. A renal biopsy exhibits focal glomerular necrosis with crescents and vasculitis affecting arterioles and venules. Which of the following best describes the renal disease of the patient?

**Core Concept**
The patient presents with a constellation of symptoms and laboratory findings suggestive of a systemic vasculitic process involving the kidneys, lungs, and nasal passages. The presence of C-ANCA (antineutrophil cytoplasmic antibody) and the renal biopsy findings are key clues to the underlying disease process.

**Why the Correct Answer is Right**
The patient's symptoms and laboratory findings are consistent with Granulomatosis with Polyangiitis (GPA), formerly known as Wegener's Granulomatosis. GPA is a form of small vessel vasculitis that affects the kidneys, lungs, and upper respiratory tract. The presence of C-ANCA, which targets proteinase 3 (PR3), is a hallmark of GPA. The renal biopsy findings of focal glomerular necrosis with crescents and vasculitis affecting arterioles and venules are also characteristic of GPA. The lack of eosinophilia and the presence of hematuria and red blood cell casts further support this diagnosis.

**Why Each Wrong Option is Incorrect**

**Option A:** This option is incorrect because Pauci-immune glomerulonephritis is a characteristic feature of GPA, not a separate entity.
**Option B:** This option is incorrect because Goodpasture syndrome is a distinct autoimmune disease that targets the basement membrane of the lungs and kidneys, but it does not typically present with C-ANCA positivity or the same renal biopsy findings as GPA.
**Option C:** This option is incorrect because IgA nephropathy is a different form of glomerulonephritis that typically presents with episodic hematuria and is not associated with C-ANCA or the systemic vasculitis seen in GPA.
**Option D:** This option is incorrect because Membranous nephropathy is a different form of glomerulonephritis that typically presents with nephrotic syndrome and is not associated with C-ANCA or the systemic vasculitis seen in GPA.

**Clinical Pearl / High-Yield Fact**
The presence of C-ANCA positivity in a patient with renal disease and systemic symptoms should raise suspicion for GPA, a potentially life-threatening disease that requires prompt treatment with immunosuppressive therapy.

**Correct Answer:** C.

✓ Correct Answer: C. Rapidly progressive glomerulonephritis