Abstract:

Ｏｂｊｅｃｔｉｖｅ：To investigate the relationship between clinical manifestation  of renal damage with antineutrophils cytoplasmic antibody（ANCA)associated vasculitis（AAV) and serum C3.
Ｍｅｔｈｏｄｏｌｏｇｙ：Three hundred and four  patients were diagnosed as AAV in the first affiliated hospital of Xinjiang medical university from January 2010 to January 2018,and 200 patients with complete clinical data were involved in this study.They were divided into low C3 group (C3＜079 g/L，n=85) and normal C3 group (C3≥079 g/L,n=115)．Clinical characteristics,laboratory data,therapy and prognosis of two groups were compared,and the influencing factors of  end point events were analyzed.
Ｒｅｓｕｌｔｓ：The serum creatinine (SCr),24hour urine protein(24UP) and Birmingham vasculitis activity score (BVAS) in the low C3 group were higher than those in normal C3 group（P＜005）; Hemoglobin (Hb),platelet count,eGFR value,C4,creactive protein (CRP) and erythrocyte sedimentation rate in low C3 group were all lower than those in normal C3 group（P＜005）; There was no significant difference between the two groups in age,gender,ANCA type and titer,WBC and serum albumin level (P＞005)The frequency of intensive immunotherapy,renal replacement therapy and plasma pheresis in low C3 group was higher than that in normal C3 group(P＜005).KaplanMeier survival curve showed that  renal survival rate of patients in low C3 group was significantly lower(logrank=14131，P＜005).Age,24UP and Scr were higher in the endpoint events group（P＜005）.Hb,platelet number and  C3 level were also lower in endpoint events group.COX analysis suggested that age,SCr and 24UP were independent risk factors that affect the prognosis of AAV patients (P＜005).
Ｃｏｎｃｌｕｓｉｏｎ：AAV patients with C3  decline were more serious in renal involvement,with poor prognosis.Much more attention should be paid to AAV patients with low  C3 level.

Key words: anti-neutrophil cytoplasmic antibody-associated vasculitis, serum complement C3, clinical analysis