A simple competitive protein binding assay for plasma cortisol

Abstract

The availability of cortisol labelled with 75 Se has permitted the development of a simple and rapid competitive protein binding assay for cortisol. Plasma samples are diluted with water and heated at 70° to destroy endogenous transcortin, and an aliquot is then incubated with 75Se-labelled cortisol and charcoal-treated rabbit serum. Separation of the bound and free fractions is achieved by a Sephadex equilibration technique. Results compare closely with those obtained using a specific, automated fluorimetric assay. The assay is more specific and technically simpler than manual fluorimetric methods.