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An accurate and relatively simple radioimmunoassay method for the measurement of aldosterone in human plasma is described. One ml or less plasma with 3H aldosterone (2 pg) is extracted with dichloromethane. Two alternative purification steps are described, either a standard paper chromatography (B5) or a more rapid Sephadex LH-20 column (60 × 1 cm) in the system dichloromethane: methanol 98:2 provides adequate purification for analysis. The assay uses either an antibody of high specificity generated against aldosterone-18, 21-disuccinate, or the 3-oxime coupled to bovine albumin. The samples, or standards, are incubated for 1–2 hours at 5° C with dilute antibody and 3H aldostercne. Separation of bound from free aldosterone is affected with activated and coarse-graded Florisil. This one-day method, using the disuccinate antibody and the LH-20 column, is associated with blank values difficult to distinguish from zero (< 6 pg). Aldosterone values from adrenalectomized subjects or duplicate samples after cortisone addition (2 μg/100 ml) give undetectable values. Accuracy studies yield essentially a zero intercept and a slope similar to 1.0. When various plasma samples were measured by either an established double isotope derivative method or by the radioimmunoassay using either the paper or LH-20 column purification steps, the values obtained by analysis of variance were not significantly different.
Ito et al. (Sat,) studied this question.