A Population-based Study Showing Better Renal Prognosis for Proteinase 3 Antineutrophil Cytoplasmic Antibody (ANCA)-associated Nephritis Versus Myeloperoxidase ANCA-associated Nephritis

Objective. Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is usually differentiated based on clinical phenotypes, but recent data indicate that myeloperoxidase (MPO)-AAV is genetically distinct from proteinase 3 (PR3)-AAV. We reviewed a population-based cohort of AAV, focusing on differences in clinical and laboratory characteristics and to compare renal outcome between MPO-ANCA and PR3-ANCA nephritis. Methods. All new cases of AAV diagnosed between 1997 and 2009 in a geographically defined area in southern Sweden were retrieved using a validated search algorithm. Data were collected from time of diagnosis and end of followup. Renal and patient survival were analyzed according to ANCA serotype. Results. During the study period, 201 patients were diagnosed with AAV, 98 tested positive for PR3-ANCA, and 85 for MPO-ANCA. Patients with PR3-ANCA were younger, had significantly higher inflammatory activity, and had a larger number of organs involved at diagnosis, but nephritis was more prevalent among patients with MPO-associated (72/85; 85%) versus PR3-associated disease (67/98, 68%). When comparing only patients with ANCA-associated nephritis, those with MPO-ANCA were more likely to develop endstage renal disease (n = 27, 38%) than those with PR3-ANCA (n = 10, 15%), p = 0.003. The risk remained significantly elevated after adjusting for sex, age, and s-creatinine level at diagnosis (UIR. 2.64; 95% CI 1.25-5.58; p = 0.003). There were no significant differences in mortality rates between the 2 groups. Conclusion. The outcome in this population-based cohort indicates that among AAV patients with nephritis, renal prognosis is better in the PR3-ANCA group, even after adjustment for sex, age, and renal function at diagnosis.