Improved extraction of aldosterone from plasma and urine before radioimmunoassay.

Radioimmunoassay of urinary or plasma aldosterone requires an initial extraction of steroids before purification and analysis. This extraction characteristically must be performed on acid-hydrolyzed urine or plasma, both of which have been supplemented with tnitiated aldosterone, to assess the analytical recovery. After extraction, the organic phase must be washed sequentially with 0.1 mol/liter sodium hydroxide, 0.1 mol/liter acetic acid, and distilled water (1, 2), a laborious process that takes several hours. We sought an alternative, and describe here an improved extraction method for aldosterone that could be applied to other steroids.