This patient presented with rapid decline in renal function and nephritic sediment, which suggests rapidly progressive glomerulonephritis. Additionally, the pulmonary infiltrates found on this patients chest radiograph raise suspicion for a pulmonary-renal syndrome. To confirm the suspected diagnosis, the patient should undergo emergent renal biopsy. Rapidly progressive glomerulonephritis is characterized by crescent formation on light microscopy of the renal biopsy specimen.3 Immunofluorescence microscopy can distinguish between the 3 types of rapidly progressive glomerulonephritis: (1) anti-GBM disease, (2) pauci-immune glomerulonephritis, and (3) immune complex disease. Immune complex disease is associated with low complement levels and is unlikely in this patient given his normal complement levels. Both anti-GBM disease and pauci-immune glomerulonephritis can present as pulmonary-renal syndromes. On serologic testing, anti-GBM antibodies are positive in anti-GBM disease, while ANCA is positive in pauci-immune glomerulonephritis. Although these 2 diseases can be distinguished based on serology, a renal biopsy is still required because many of the currently available assays are not sufficiently accurate and the potential toxicities of current therapies for both diseases are too great to rely on serologic results alone. In anti-GBM disease, immunofluorescence microscopy of the biopsy specimen will show linear deposition of IgG along the basement membrane, whereas immunofluorescence studies are negative in pauci-immune glomerulonephritis.
- Emergent renal biopsy.
3. Jennette JC. Rapidly progressive crescentic glomerulonephritis. Kidney Int 2003;63:1164–77.
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