MO274EVALUATION OF SERUM C3 LEVELS AND C3 IMMUNOFLUORESCENCE IN PATIENTS WITH ANCA-ASSOCIATED VASCULITIS: A RETROSPECTIVE COHORT STUDY

Abstract

Abstract Background and Aims The role of complement activation, mainly alternative system, has been recently proposed to play an important role in the pathogenesis of ANCA associated vasculitis (AAV). Real life data assessing its predictive role in renal outcomes are limited. In this study, we evaluated the value of serum and kidney deposited C3 in predicting renal outcomes in patients with AAV. Method In this retrospective study, patients with AAV were categorized according to their baseline serum C3 levels as hypo- or normo-complementemic and to those with positive or negative kidney biopsy immunofluorescence (IF) for C3. Clinical, serologic, treatment and histopathologic characteristics, as well as prognosis between the 2 groups were compared. Results: Forty-seven patients (51% men) were enrolled with a mean age at diagnosis of 65 years and were followed up for a median period of 56 months. At baseline, 23% (11/47) of the patients were hypocomplementemic (C3 <75 mg/dL). These patients were older (74 vs. 65 years,p=0.013), had higher creatinine levels (4.9 vs. 2.2 mg/dL, p=0.006), were more often hemodialysis dependent (64% vs. 19%, p=0.009) and progressed more often to ESRD (55% vs .11%,p=0.01) compared to normo-complementemic patients (n=36). On multivariate analysis, serum Cr at diagnosis (HR=16.8, 95%CI: 1.354-208.62,p=0.028) and low serum C3 (HR=2.492; 95% CI: 1.537-11.567,p=0.044) were independent predictors for ESRD. Among 25 patients with kidney biopsy data, those with positive IF staining for C3 (56%, n=14) had more often a mixed histological pattern (72% vs. 27%,p=0.033), low serum C3 levels (42% vs. 18%,p<0.001) and serious infections during follow-up (57% vs. 18%,p=0.047) compared to those with negative (n=11) IF staining. Conclusion Low serum C3 levels at diagnosis may be an independent prognostic factor for ESRD progression in patients with AAV. This should be taken into account in therapeutic and monitoring strategies.