Measurement of Plasma Aldosterone by Radioimmunoassay

A linear relationship between amounts of aldosterone measured and the size of the samples confirmed accuracy and 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.

Abstract

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.