Nonchromatographic Radioimmunoassay of Plasma 11-Deoxycortisol, for Use in the Metyrapone Test, with Polyethylene Glycol as the Precipitant

Abstract

Abstract We have developed a simple, reliable radioimmunoassay for plasma 11-deoxycortisol. The method does not require chromatography but instead makes use of a simple extraction procedure which, in combination with the antibody characteristics, is highly specific for the metyrapone test. Polyethylene glycol was used to separate free and antibody-bound steroid. The smallest amount measurable is 15 pg (2.0 µg/ liter of plasma). The method is shown to be precise and accurate. Intra-assay precision of the method for two plasma pools was 26.7 ± 2.5 µg/ liter (CV = 9.4%) and 61.2 ± 3.7 µg/ liter (CV = 6.0%). The respective inter-assay precision was 27.0 ± 1.7 µg/ liter (CV = 6.3%) and 59.9 ± 2.3 µg/ liter (CV = 3.8%). The validity of the assay was further verified by evaluating the plasma 11-deoxycortisol response to metyrapone administration. The relative simplicity of the method and the commercial availability of all reagents, including antisera, makes this radioimmunoassay procedure practical for use in clinical laboratories.