Solid phase radioimmunoassay for the determination of aldosterone excretion

A solid phase radioimmunoassay (SP-RIA) was developed for the determination of urinary conjugated aldosterone. Acid-hydrolyzed urine was extracted with dichloromethane and the extract was analyzed by SP-RIA. Microtiter plates were coated with two different anti-aldosterone antisera (S-3: against aldosterone-21-hemisuccinate-BSA and 58: aldosterone-3-(O-carboxymethyl)-oxime-BSA separately and preincubated with 3H-aldosterone. Reference values were obtained using a liquid radioimmunoassay method including paper chromatography. Regression analysis revealed for S-3: Y = 0.8 X + 3.2, r = 0.84; p < 0.0001; n = 36 and for 58: Y = 1.16 X + 1.2, r = 0.89; p < 0.0001; n = 36. The SP-RIA assay is useful for routine measurement of conjugated aldosterone excretion. The method is time-saving and does not require paper chromatography, and is adequate for many clinical purposes.