Clinical application of insulin enzymoimmunoassay: its comparison with radioimmunoassay

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Enzymoimmunoassay (EIA) using sandwich method with insulin antibody bound beads and insulin antibody bound peroxidase was compared with radioimmunoassay (RIA) in the determination of insulin of human sera. The substrate solution comprised hydrogen peroxide and 5-aminosalicylic acid. The following results were observed: (1) The sensitivity of EIA was 5μU/ml, comparable to that of RIA. The linearity of the standard curve was obtained between 0 and 160μU/ml insulin. (2) The coefficient of variation of the intra-EIA was 14.2% at about 16μU/ml insulin and 7.5% at about 35μU/ml insulin, while that of inter-EIA 9.7% and 5.8%, respectively, which had not great difference from that of RIA. (3) The coefficient of correlation of insulin determined by EIA (Y) and RIA (X) in 170 human sera obtained at 50g oral glucose tolerarlce test was 0.918 (p<0.001) and the regression equation was Y=1.110x-4.278. (4) Proinsulin interfered with EIA, while C-peptide did not. (5) Hypoproteinemic sera revealed the discrepancy between EIA and RIA. The insulin ElA was suggested to be apPlicable clinically, although further study on its validity was needed.