Development of an ELISA for urinary cystatin C and its application in diabetic nephropathy

Objective To develop an enzym linked immuno sorbent assay (ELISA) for urinary cystatin C(Cys C) in order to evaluate its clinical significance in diabetic nephropathy (DN). Methods Assay the level of urinary and serum Cys C in 129 normal peoples, 55 patients with diabetic mellitus(DM) and 59 patients with DN. 59 DN patients were divided into two groups according to different urinary albumin(Alb) excretion, 30～300 mg/24 h(group A, 39 patients) and Alb300 mg/24 h(group B, 20 patients). Results The detection limit of this assay was 0.283 μg/L. The working range was 0.39-25.0 μg/L. The urinary Cys C was significantly higher in A group than normal group (P0.01). But the serum Cys C did not differ significantly between them(P0.05). The level of serum and urinary Cys C were also obviously higher in B group than A group(P0.01). The area of serum and urinary Cys C under the ROC curve of A group were 0.448±0.081 and 0.811±0.055, and the area of that under the ROC curve of B group were 0.813±0.060 and 0.928±0.037. Conclusions The ELISA for urinary Cys C had high sensitivity ,stability and accuracy. And it could be regard as a high sensitive and specific marker in DN.