Kidney Week

Abstract: PUB142

When Serology Misleads: Double-Positive ANCA and Anti-GBM with Monoclonal Protein Without Active Glomerulonephritis

Session Information

• Publication Only

Category: Glomerular Diseases

• 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics

Authors

• Afzal, Aurangzeb, Virginia Commonwealth University, Richmond, Virginia, United States

Aurangzeb Afzal, MD

• Gizaw, Andinet, Virginia Commonwealth University, Richmond, Virginia, United States

Andinet Gizaw, MD

• Fatani, Imran F., Virginia Commonwealth University, Richmond, Virginia, United States

Imran F. Fatani, MD

• Kidd, Jason M., Virginia Commonwealth University, Richmond, Virginia, United States

Jason M. Kidd, MD, FASN

• Muthusamy, Selvaraj, Virginia Commonwealth University, Richmond, Virginia, United States

Selvaraj Muthusamy, MBBS, PhD, FASN

Introduction

Pulmonary-renal syndrome is classically associated with ANCA-associated vasculitis and anti-glomerular basement membrane disease. However, double-positive serology and monoclonal proteins may not reflect active disease, particularly when urine, pulmonary, and biopsy findings are discordant.

Case Description

A 74-year-old woman presented with cellulitis and severe hyponatremia with preserved kidney function and bland urinalysis. During hospitalization, she developed rapidly progressive acute kidney injury (creatinine peak 4.3 mg/dL) and hypoxic respiratory failure with bilateral infiltrates and pleural effusions. Outside testing showed c-ANCA positivity (1:80) with mildly elevated PR3 and MPO antibodies and weakly positive anti-GBM antibody, raising concern for double-positive pulmonary-renal syndrome and prompting corticosteroids and plasmapheresis.
At a tertiary center, urine microscopy showed no dysmorphic red blood cells or casts, and bronchoscopy showed no diffuse alveolar hemorrhage. Repeat ANCA and anti-GBM testing, obtained after plasmapheresis initiation, were already low/negative after a single session and remained negative. Complement levels were low-normal to normal, without a pattern suggestive of immune-complex glomerulonephritis. Monoclonal studies revealed a faint lambda band, raising concern for monoclonal gammopathy-related kidney disease; however, biopsy showed global glomerulosclerosis with old fibrous crescents, focal scarring, interstitial fibrosis/tubular atrophy, and mild–moderate acute tubular injury, without cellular or fibrocellular crescents, necrosis, vasculitis, or monoclonal deposition.
Plasmapheresis was discontinued. The patient required kidney replacement therapy and was transitioned to comfort care

Discussion

This case represents a pulmonary-renal syndrome mimic with serologic–histologic discordance. Despite double-positive ANCA and anti-GBM serologies and a monoclonal protein, biopsy showed fibrous crescents and acute tubular injury without active glomerulonephritis or monoclonal deposition. Fibrous crescents indicate chronic healed injury. Absence of nephritic urine sediment and diffuse alveolar hemorrhage argues against vasculitis. Serologic findings require confirmation by biopsy.