Plasma Corticosteroids Determined by Use of Corticosteroid-Binding Globulin and Dextran-Coated Charcoal

Abstract

Corticosteroid-binding globulin (CBG) and dextran-coated charcoal have been employed to measure the concentration of unconjugated corticosteroids in plasma. One ml of alkalinized plasma is extracted with methylene chloride and the extract is washed with water. The extract is dried, dissolved in a standard plasma pool containing 4-14C-cortisol, and then shaken with dextran-coated charcoal to separate protein-bound and unbound cortisol. The charcoal suspension is centrifuged. The radioactivity in the supernatant, which is extracted and counted, is inversely related to the amount of unconjugated corticosteroids in the original plasma. The specificity of the CBG-charcoal method as a measure of cortisol in plasma depends on 2 factors: the limited binding of most steroids other than cortisol by CBG and the low concentrations of all unconjugated steroids other than cortisol in normal human plasma. The method has a high degree of precision and accuracy. The results of analyses of plasma for corticosteroids using the CBG-charcoal method agreed closely with those obtained by using a chromatographic-fluorometric technique which specifically measures cortisol.