A simplified radioimmunoassay for plasma aldosterone.

The analytical evaluation is described of a [125I]-aldosterone radioimmunoassay method for measuring aldosterone in human plasma, which requires no chromatographic purification before quantification by radioimmunoassay but does require organic solvent extraction. Rabbit anti-aldosterone serum is used, generated against aldosterone-3-oxime coupled to thyroglobulin. The antibody demonstrates negligible cross reactions with structurally-related steroids. The proposed method uses [125I]-labeled aldosterone as the radioactive ligand. The recovery of D-aldosterone added to human plasma averaged 98 percent. The parallelism and precision of the method are excellent. Seventy specimens were assayed by the proposed method and a [3H]-aldosterone reference procedure, which includes LH-20 column chromatographic purification prior to the radioimmunoassay step (y = 1.03X - 3.0; r = 0.99; p less than 0.01). The [3H]-aldosterone reference procedure uses an anti-aldosterone serum prepared against aldosterone-3-oxime coupled to rabbit serum albumin.