A direct radioimmunoassay for free aldosterone in urine without extraction and chromatography

A direct radioimmunoassay for the determination of free (unconjugated) aldosterone in urine has been developed for the clinical laboratory. The method is based on a determination without extraction and chromatography. In comparison with a reference method including extraction and column chromatography on Sephadex LH 20 a highly significant correlation was found. The coefficient of variation was 5.6 % for intraassay variability and 10.4 % for interassay determinations. In normal adults the average value of the urinary free aldosterone was 190 ng/24 h (range: 60-320 ng/24 h). During sodium restriction, a 3 fold increase in free aldosterone was observed in normal subjects. In patients with adrenal insufficiency, the values were below 60 ng/ 24 h, and in two patients with Conn's syndrome, the excretion of free aldosterone was 890 and 1040 ng/24 h. The method was found suitable for routine clinical use. (author)