Re‐evaluation of the captopril test for the diagnosis of primary hyperaldosteronism

OBJECTIVE: We aimed to re-evaluate the captopril test in the diagnosis of primary hyperaldosteronism. DESIGN: Serum aldosterone and plasma renin activity were measured supine prior to and 60, 90, 120 minutes after oral captopril, 25 mg. PATIENTS: We have performed this test in ten patients with primary hyperaldosteronism, two with hypertension and secondary hyperaldosteronism and in ten normokalaemic patients with essential hypertension. MEASUREMENTS: Validity was assessed by mathematical prediction methods. RESULTS: Using a ratio of aldosterone to plasma renin activity greater than or equal to 1400 pmol/l per microgram/ml/h as a predictor of primary hyperaldosteronism, the captopril test had a sensitivity of 100%, a specificity of 83% and a predictive value of 82% with a 60-minute post captopril evaluation being sufficient. Nevertheless, this test was only marginally superior to a careful analysis of the supine values where a similar ratio in the presence of a normal or suppressed plasma renin activity predicted primary hyperaldosteronism with a sensitivity also of 100% but a slightly lower specificity of 75% and predictive value of 77%. CONCLUSION: Application of the captopril test to patients identified as abnormal by screening confirms all cases of primary hyperaldosteronism but false positive or equivocal results, necessitating further investigation, may occur in some patients with essential hypertension.