Serum C3 complement levels in ANCA associated vasculitis at diagnosis is a predictor of patient and renal outcome

Aim To determinate the prognostic significance of low serum C3 at the time of diagnosis of ANCA-associated vasculitis (AAV). Methods Our cohort included 75 consecutive patients with AAV diagnosed from January 2005 to December 2015. C3 levels were measured at the time of diagnosis. Patients were divided into two groups, those with low serum C3 levels (< 0.9 g/l) and those with normal serum C3 levels (0.9-1.8 g/l). We analysed association between serum C3 levels and both combined and singularly patient and renal survival (ESRD). Small number of relapsed patients did not allow for the statistical analysis to be performed as to weather the low serum C3 is associated with relapse rate in AAV patients. Results Low serum C3 levels were significantly associated with worse combined end-point patient and renal survival (HR 3.079; 95% CI 1.231-7.701; p = 0.016), and on multivariate adjusted analysis association remained significant (HR 2.831; 95% CI 1.093-7.338; p = 0.032). For both end-points individually low serum C3 levels were significantly associated with poorer patient survival (HR 6.378; 95% CI 2.252-18.065; p < 0.001; on multivariate adjusted analysis HR 4.315 95% CI 1.350-13.799; p = 0.014) and renal survival (HR 3.207; 95% CI 1.040-9.830; p = 0.043; on multivariate adjusted analysis HR 3.679; 95% CI 1.144-11.827; p = 0.029). In our study there was no significant association between serological and patohistological phenotypes and serum C3 levels. Conclusion Lower serum C3 levels at the diagnosis is associated with poorer patient and renal outcomes in AAV patients.