Measurement of Plasma Aldosterone by Radioimmunoassay

A radioimmunoassay for the measurement of plasma aldosterone is described. Aldosterone-3-carboxymethoxime-18,21-diacetate was coupled with rabbit albumin and antibodies produced in rabbits. Five to 20 ml of plasma, with l,2-3H-aldosterone added for recovery, was extracted and purification achieved by one paper chromatography. After 20 min incubation of the antibody-steroid mixture at 37 C, bound and free fractions were separated using Florisil. The mean recovery of 3H-aldosterone, after extraction and chromatography, was 66.3 ± 13.6 (sd)%. The specificity of the method was confirmed by comparing the results obtained with those of the double isotope derivative method on the same plasma samples. The nonspecific blank was 0.088 ± 0.055 ng/sample (mean ±sd). A linear relationship between amounts of aldosterone measured and the size of the samples confirmed accuracy. Coefficients of variation of 14, 13.2 and 10.5% were obtained at levels of 4, 18 and 51 ng of aldosterone/100 ml of plasma. Results on normal individuals were comparable to those in the literature.