Objective To develop a highly sensitive and specific ELISA to detect the human serum intact insulin and to explore the relationgship between true insulin and cardiovascular risk factors clustering in a population-based epidemiological study.Methods The assay was based on two monoclonal antibodies,one bound to microtitre plate as the antibody in solid phase and the other was biotinated as the antibody inliquid phase.The biotin-avidin ELISA was used to measure the serum intact insulin of 1196 subjects aged 35 to 59 in Pizhou city,Jiangsu Province.Results With a detection limit of 0.63mIU/L,the ELISA covered linear calibrator in the range of 0~0.63 mIU/L.There was no crossreaction of human proinsulin and C-peptide at 142 and 3 960 pmol/L respectively.The mean recovery rate was 97.12%.The CV of intra- and inter-assay were less than 8.23% and 3.74%respectively.The results of population-based epidemiological study indicated that the concentration of intact insulin was significantly different between male and female and the medians were 4.24(2.57~6.57)and 5.45(3.50~7.46) mIU/L respectively.However,no significant difference was found among various age group.Furthermore,the significantly positive level of true insulin correlated with BMI, WC, SBP, DBP, CH, TG,cardiovascular risk factors clustering,while the significantly negative associated with HDL-ch.Conclusions The monoclonal-based BA-ELISA can be used to detect serum intact insulin in the clinical and epidemiological study.Insulin resistance emerges as a common pathogenetic denominator underlying the risk factor clustering and the deficiency of nonesterified fatty acids metabolism has been implicated as the cause of abnormal lipid and glucose metabolism