This prospective study was designed to compare the captopril suppression test with the salt-loading approach to confirm the diagnosis of primary aldosteronism. A total of 49 patients were referred with a presumed diagnosis of primary aldosteronism. The captopril test was performed in the morning with patients in the seated position after overnight fasting. Blood samples for plasma aldosterone were obtained before captopril administration (25 mg PO) and again 2 hours later. Patients were then subjected to a high salt diet (300 mmol sodium per day for 3 days). On the third day, urinary sodium (24 hours) was measured, and plasma aldosterone levels were measured at 8:00 am (recumbent) and at noon (standing). Of the 49 patients, 44 had nonsuppressible aldosterone concentrations with all the clinical characteristics of primary aldosteronism: 22 patients had surgically confirmed unique adenoma, and 22 patients had presumed bilateral hyperplasia. There was a significant correlation between plasma aldosterone values of salt-loaded patients (mean of 8:00 am and noon results) and the values 2 hours after captopril administration (r=0.8, P<0.01). Plasma aldosterone cumulative distribution curves in primary aldosteronism patients (adenoma and hyperplasia) were not significantly different between the 2 suppression tests. Our results showed that the captopril suppression test is as effective as sodium loading in confirming the diagnosis of primary aldosteronism.
