Radioimmunoassay for Aldosterone Without Chromatography

A radioimmunoassay for the determination of urinary aldosterone-18-glucuronide has been developed for the clinical laboratory. Ten ml of urine is pre-extracted with methylene chloride and then submitted to acid hydrolysis. This is followed by a second methylene chloride extraction. The aldosterone concentration in these extracts is determined with antisera obtained from rabbits immunized with an aldosterone-oxime bovine gamma globulin conjugate. In view of the high recovery of [1,2- 3 H] aldosterone no internal indicator standards were used. The sensitivity of the overall assay was 0.44 μg/24 h. The coefficient of variation was 3.7 % within a single assay and 13.6 % for multiple assays. The specificity of the method was examined by comparison with a double isotope dilution derivative method and by simultaneous use of 6 different antisera. Under normal sodium intake the urinary excretion of the acid-labile aldosterone-18-glucuronide ranged from 4.0 to 13.0 μg/24 h in 9 normal male subjects.