Background: Patients have been described who have both anti-neutrophil cytoplasm antibodies (ANCA) and anti-glomerular basement membrane (GBM) antibodies. We have attempted to define the true prevalence of such "double positive" patients, and describe in detail their clinical features and outcome.
Methods: We have reviewed all serologic assays performed between 1990 and 2000 in a single institution, and the case notes of patients having sera positive for both ANCA and anti-GBM antibodies. During this time 20,392 sera were initially tested for ANCA, and 4808 sera tested for anti-GBM antibodies.
Results: Five percent of all ANCA-positive serum samples were also positive for anti-GBM antibodies, and 32% of all anti-GBM positive samples had detectable ANCA. Of 27 patients with both antibodies, 82% had anti-myeloperoxidase specific P-ANCA. Pulmonary hemorrhage occurred in 44%. Renal biopsy showed extensive glomerular cellular crescents in most patients. Patient and renal survival rates were 52% and 26%, respectively, at one year. Sixty-eight percent of patients were dialysis-dependent at presentation, and none of these recovered renal function, despite immunosuppression with or without plasma exchange.
Conclusion: Serologic evidence of double positivity for both ANCA and anti-GBM antibodies is common in patients with either antibody. In our study these patients have a poor prognosis when presenting with severe disease and initially behave more like anti-GBM disease than vasculitis. Recovery from severe renal failure is rare.