Direct radioimmunoassay of plasma aldosterone in normal subjects.

A direct radioimmunoassay of plasma aldosterone concentration using an antibody of high specificity is described and compared to a previous chromatographic radioimmunoassay. A significant correlation was found between the plasma aldosterone concentration determined by this direct radioimmunoassay and by a radioimmunoassay including paper chromatography in 38 plasma samples obtained from patients with hypertension of various etiology. This direct radioimmunoassay of plasma aldosterone concentration is simpler and less time-consuming. A significant and similar correlation between plasma aldosterone concentration and plasma renin activity (active renin) and renin concentration (total renin) was found in normal subjects on a regular and a low sodium intake. Plasma aldosterone concentration in normal subjects was significantly and negatively related to age and to the 24-h urinary sodium excretion.