Detection of primary aldosteronism using the captopril test

In order to evaluate whether changes in the plasma concentration of aldosterone (PA) following the administration of captopril, an inhibitor of angiotensin-converting enzyme, will establish the diagnosis of primary aldosteronism we have used this test in 9 healthy subjects and in 22 patients with various forms of hypertension, including 5 patients with primary aldosteronism due to idiopathic adrenal hyperplasia (n = 4) or aldosterone-producing adenoma (n = 1). The response of PA to captopril (25 mg orally) was investigated on an outpatient basis, following a rest period of 120 minutes in the supine position. In healthy subjects PA decreased from a mean basal value of 11.5 +/- 5.9 ng/dl to less than 6.4 ng/dl (4.9 +/- 1.4 ng/dl p less than 0.01]). Similarly, captopril induced a fall in PA concentration to less than 6.4 ng/dl in patients with essential hypertension, with renal artery stenosis or with an afunctional kidney. Post-captopril concentrations of plasma aldosterone were about twice the normal level in 3 of 4 patients with idiopathic adrenal hyperplasia and about four-fold raised above normal in the patient with an aldosterone-producing adenoma. In spite of a false-negative result in one patient with idiopathic adrenal hyperplasia, the administration of captopril appears to be of use in recognizing patients with primary aldosteronism on an outpatient basis.