Simultaneous enzyme immunoassay of cortisol and dehydroepiandrostone-sulphate from a single serum sample using a transferable solid phase system.

An enzyme immunological methodology for the direct and simultaneous estimation of serum cortisol and dehydroepiandrosterone-sulphate (DHEA-S) useful for the biochemical differential diagnosis of Cushing's syndrome has been developed. The combined estimation of both steroids is more economical in time, work and materials than two separate assays. Two solid phases, a microtitre plate and a covering transferable needle lid system were used in the present procedure. Both solid phases are first coated with anti-rabbit IgG and then each with a specific antiserum. Horseradish peroxidase was used as marker enzyme and tetramethylbenzidine as the chromogen for measuring enzyme activity. No extraction or deproteinization steps are involved. The turn around time for 41 samples (in duplicate) is 3 h. The detection limit of the assay is 5 pg/well for cortisol and 10 pg/well for DHEA-S. Results of the present method correlated well (cortisol, r = 0.95; DHEA-S, r = 0.98) with those of commercial radioimmunoassays using iodinated labels. Thus, this technique offers a convenient non-isotopic procedure in the routine clinical laboratory.