[A simplified radioimmunoassay for serum aldosterone--non-extraction method with 125I-labeled aldosterone (author's...

A simplified direct radioimmunoassay system for serum aldosterone measurement was developed by using radio iodine-labeled aldosterone and highly specific antiserum to aldosterone. 8-anilino-1-naphthalene sulfonic acid(ANS) was used to prevent the binding of aldosterone to serum proteins. Polyethylene glycol was used to separate the antibody-bound aldosterone from the free aldosterone as the precipitant. The minimum measurable concentration of aldosterone is 30pg/ml of serum by short incubation method (at 25 degrees C for 3hr incubation) and 15pg/ml of serum by long incubation method (at 4 degrees C for 20 hr incubation) respectively. Present radioimmunoassay eliminates extraction of the aldosterone from serum and chromatographic separation procedures, and requires only 0.1ml of serum sample for assay. The intra-assay precision was C. V. 6.9% (average of 4 samples) and the inter-assay precision was C. V. 10.7% (average of 4 samples). There is an excellent correlation between the extraction method and this direct method in serum aldosterone value obtained (correlation coefficient, 0.96). The normal value was 36.8+/-25.9pg/ml (recumbent) and 113.6+/-6.15pg/ml (upright).