Development and application of a simple radioimmunoassay for urinary aldosterone

A simple, economical and direct assay was developed to measure aldosterone in urine, using aldosterone antibody of high specificity and gamma labelled ligand. The assay allows the direct measurement of aldosterone in 100 microliters aliquots of urine after acid hydrolysis. It does not require preliminary solvent extraction and purification steps and hence a large number of samples in a single batch can be assayed simultaneously. An excellent correlation was obtained between the results of the direct assay and the levels measured after extraction and paper chromatography. (Y = 0.97X + 0.89, r = 0.99, p less than 0.001) or after extraction alone (Y = 0.98X + 1.75, r = 0.99, p less than 0.001). The coefficients of variation for inter-assay and intra-assay determinations of samples from normal and high urine pools were 4.2-6.5% and 5.6-9.8%, respectively. Total urinary aldosterone excretion in 21 normal subjects on unrestricted sodium diet ranged from 3.8-20.2 micrograms/24 h (10.5-55.0 nmol/24 h) with a mean of 12.5 +/- 4.6 (SD) micrograms/24 h (34.7 +/- 12.8 (SD) nmol/24h).