Double antibody enzyme immunoassay of cortisol in bovine plasma

A double antibody enzyme immunoassay of plasma cortisol was established using beta-galactosidase from E. coli as the tracer. Cortisol-21-hemisuccinate was conjugated with beta-galactosidase using a water-soluble carbodiimide. An antibody raised in the rabbit against cortisol-21-hemisuccinate-bovine serum albumin was used as the first antibody and anti-rabbit gamma-globulin goat serum was used as the second. The sensitivity of the present enzyme immunoassay was 25 pg/tube. The method satisfied general reliability criteria regarding specificity, accuracy and precision. Plasma cortisol levels estimated by the enzyme immunoassay was highly correlated (r = 0.99, P less than 0.005) with the levels measured by radioimmunoassay. This method of enzyme immunoassay was found to be of practical application to the routine assay of plasma cortisol.