Comparison of an enzyme-linked immunosorbent assay (ELISA) with a radioimmunoassay (RIA) for the measurement of rat insulin.

A recently developed competitive enzyme-linked immunosorbent assay (ELISA) was compared with a conventional competitive radioimmunoassay (RIA) for the measurement of rat insulin in culture medium. Fifty-six samples were analysed by both assays. There was a correlation coefficient of r = 0.783 between results obtained using the two assay systems. The binding curves of the two assays were differently shaped, so that the ELISA gave good reproducibility over the concentration range 5-50 microU/ml insulin with inter- and intra-assay coefficients of variation less than 14%, but poor reproducibility at higher concentrations. Conversely, the RIA showed excellent reproducibility at concentrations greater than 50 microU/ml insulin, but poor sensitivity and high coefficients of variation below this level. The ELISA procedure offers practical advantages over the RIA, and performs well when measuring physiological concentrations of insulin.