AB0391 LOW SERUM COMPLEMENT C3 LEVEL AS A RISK FACTOR FOR RELAPSE OF ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS: A RETROSPECTIVE COHORT STUDY

Abstract

Background:The alternative pathway of complement activation has recently been recognized as a key pathogenic event in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Some previous studies have reported that low serum complement C3 level in AAV patients is associated with more severe renal disease, worse renal prognosis, or higher mortality. However, the correlation between low serum C3 level and AAV relapse remains unclear.Objectives:To analyze the clinical characteristics and outcomes of AAV patients with low serum C3 levels at the time of diagnosis.Methods:We conducted a retrospective observational cohort study including 83 consecutive patients diagnosed with AAV in our hospital from January 1999 to December 2020. Serum C3 levels were measured at diagnosis. AAV included microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA); patients with ANCA-negative AAV were excluded. Patients were divided into low- and high-C3 groups (C3 < 100 and ≥ 100 mg/dL, respectively). We compared the clinical characteristics, and relapse-free and overall survival rates, of the two groups, and identified predictors of AAV relapse.Results:Of the 83 patients (MPA, n = 61; GPA, n = 18; EGPA, n = 4), 20 (24%) were in the low-C3 group. We found no significant group difference in sex, body mass index, disease type, ANCA subtype, Birmingham Vasculitis Activity Score (BVAS), or treatment. The low-C3 group patients were older (p=0.01), and had a higher Five Factor Score (FFS) (p=0.01) and a lower remission rate (p=0.02), than the high-C3 group. The generalized Wilcoxon test revealed that the relapse-free survival time was significantly shorter in the low-C3 group (29 months; 95% confidence interval [CI]: 15–49) than in the high-C3 group (82 months; 95% CI: 61–NA; p=0.01) (Figure 1A). The overall survival was also shorter in the low-C3 group (83 months; 95% CI: 8-121) than in the high-C3 group (112 months; 95% CI: 77-NA; p=0.03) (Figure 1B). In the Cox proportional hazards model, a low C3 level (< 100 mg/dL) (hazard ratio [HR], 3.01; 95% CI: 1.29–7.04], p=0.01) and GPA (HR, 3.04; 95% CI: 1.32–7.01; p=0.01) were independent predictors of AAV relapse.Figure 1.Kaplan-Meier estimates of the relapse-free (A) and overall (B) survival rates of AAV patients by baseline serum C3 levels. Eight patients who did not show remission were excluded in the relapse-free survival analysis. Black line: high-C3 group (≥ 100 mg/dL); red line: low-C3 group (< 100 mg/dL).Conclusion:AAV patients with low C3 levels at diagnosis were at higher risk of relapse. Larger prospective studies are required to confirm these findings.Disclosure of Interests:None declared