18-Hydroxycorticosterone as a marker for primary hyperaldosteronism.

An assay for the measurement of 18-hydroxycorticosterone (18-OHB) in plasma has been validated. The method involves extraction of plasma with dichloromethane, thin layer chromatography and radioimmunoassay with an iodinated 18-hydroxycorticosterone-3-carboxymethyloxime ligand. The plasma concentration of 18-OHB was measured in 16 patients with primary hyperaldosteronism and 20 control subjects. After overnight recumbency a significantly higher mean concentration of 18-OHB was found in the samples taken from the patients than in those from the control subjects. The degree of elevation did not clearly discriminate between patients with a unilateral adenoma and those with bilateral adrenal hyperplasia. A significant anomalous postural decrease in the 18-OHB concentration occurred in 10 of the 13 patients with an adenoma, whereas there was a significant postural increase in the three patients with hyperplasia.