Nonchromatographic radioimmunoassay of plasma 11-deoxycortisol, for use in the metyrapone test, with polyethylene glycol as the precipant.

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 mug/liter of plasma). The method is shown to be precise and accurate. Intraassay precision of the method for two plasma pools was 26.7 plus or minus 2.5 mug/liter (CV equals 9.4%) and 61.2 plus or minus 3.7 mug/liter (CV equals 6.0%). The respective inter-assay precision was 27.0 plus or minus 1.7 mug/liter (CV equals 6.3%) and 59.9 plus or minus 2.3 mug/liter (CV equals 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.