Development of an enzyme immunoassay for urinary collagen IV and its application in diabetic nephropathy

Objective To develop an enzyme immunoassay for urinary collagen Ⅳ(ⅣC) in order to evaluate the metabolism of renal glomerular basement membranes and for the diagnosis of diabetic nephropathy(DN). Methods To determine the levels of serum ⅣC and urinary ⅣC in 50 normal peoples and 127 type Ⅱ diabetes mellitus(DM) patients divided into three groups according to the urinary albumin excretion(UAE): UAE30 mg/ml(group A), 30 mg/ml UAE300 mg/ml(group B), UAE300 mg/ml(group C). Results The detection limit of ELISA was 1.2 ng/ml; The within run CV was 5.4%-10.6%, the between run CV was 7.8%- 18.5% . The positive rates of urinary ⅣC(28.3%) and serum ⅣC(31.7%) were obviously higher in group A than that in control group( P 0.01 ); The positive rate of urinary ⅣC(63.2%) was significantly higher in group C (18 DM patients were complicated by DN) than that in group A (28.3%) ( P 0.01 ). The positive rate of serum ⅣC had no difference between two groups(36.8%, 31.7%) ( P 0.05). Conclusions We have developed a sensitive and simple ELISA for ⅣC. The increased urinary ⅣC level in DM patients could be a sensitive and specific marker of DN.