Implication of decreased serum complement 3 in patients with diabetic nephropathy

The serum complement 3 (C3) level was reduced in many patients with type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN). However, the clinical implications of such change are still less understood. This study was aimed to explore the association between C3 level and the baseline clinicopathological characteristics and the prognosis of T2DM patients with DN.A total of 171 T2DM patients with biopsy-proven DN who received follow-up for at least 1 year were recruited. The patients were divided into two groups based on the C3 level: decreased C3 group: < 90 mg/dl (n = 75) and normal C3 group: ≥ 90 mg/dl (n = 96). Renal outcomes were defined by progression to end-stage renal disease (ESRD) or doubling of serum creatinine (D-SCr) level. The influence of serum C3 level on renal outcomes was estimated using Cox regression.The patients with decreased C3 level had more severe renal insufficiency and glomerular lesions than those in the normal C3 group. During a follow-up period (12-78 months), 51 patients with decreased C3 levels (68.0%) and 36 individuals with normal C3 levels (37.5%) reached the endpoint. The univariate Cox regression indicated that patients in the decreased C3 group had a higher rate of the renal outcomes than patients in the normal C3 group (HR 1.897, 95% CI 1.235-2.913, p = 0.003). But the multivariate COX analysis indicated that the C3 level was not an independent risk factor for progression to ESRD and/or D-SCr (HR 1.389, 95% CI 0.847-2.278, p = 0.193) when adjusting for important clinical variables and pathological findings.Decreased serum C3 level was significantly associated with more severe renal insufficiency, higher glomerular grading and poor renal outcomes, though it failed to be an independent risk factor in T2DM patients with DN.