A Non-Chromatographic Radioimmunoassay for Plasma Dexamethasone

Abstract

A non-chromatographic radioimmunoassay for plasma dexamethasone is presented. Corticosteroid binding protein (CGB) was used to bind endogenous steroids, and free dexamethasone was adsorbed with Florisil. The purified sample was assayed by using an antiserum to dexamethasone-21-BSA. The plasma blank was less than 10 pg. When 0.1ml of plasma containing 20ng of cortisol was measured, the blank could not be differentiated from charcoal treated plasma. ³H-dexamethasone recovery from purification procedures was 33.2±4.4%. Accuracy and precision were satisfactory. Plasma dexamethasone concentrations in patients receiving dexamethasone administration are also reported.