Development of radioimmunoassays for the measurement of aldosterone in unprocessed plasma and simple plasma extracts.

Inexpensive and rapid radioimmunoassay techniques for the measurement of aldosterone in unprocessed plasma and simple plasma extracts are described. The use of low pH (pH 5.0) and merthiolate to minimise plasma protein binding and the use of aldosterone-free plasma in the standards allows the measurement of aldosterone in 50 microliter of unprocessed plasma, which has been found useful in the diagnostic screening and classification of hyperaldosteronism. Despite quantitative recovery of added (+)-aldosterone and high specificity, the aldosterone content of unprocessed plasma is overestimated, probably by the presence of a water-soluble compound which closely resembles aldosterone. The use of a simple preliminary dichloromethane extraction procedure gives an excellent correlation with values obtained after chromatography. Values are given for chosen normal people and people with benign essential hypertension, using both assay procedures in three different physiological contexts.