Comparison of confirmatory tests for the diagnosis of primary aldosteronism

Context: Primary aldosteronism (PA) is the most frequent form of secondary hypertension, accounting for up to 5-10% of all hypertensive patients, and the diagnosis of PA can present an important challenge for the clinician. After a positive screening test, the diagnosis is confirmed by a suppression test, often an iv saline load test (SLT) or a fludrocortisone suppression test (FST). The FST is considered by many to be the most reliable but is more complex and expensive. Objective and Design: Our objective was to compare the specificity of SLT with FST for the diagnosis of PA. Patients and Setting: The study included 100 hypertensive patients referred to hypertension units with suspected PA after the screening test. Intervention: All patients underwent FST and SLT. Main Outcome Measures: We assessed plasma aldosterone concentrations (PAC) before and after FST and SLT. Results: After iv SLT, 10.4% of the PA patients were negative and 16.1% of patients with essential hypertension were positive after SLT; that is, a correct diagnosis with SLT was obtained in 88% of patients compared with FST. PAC after SLT and PAC after FST were highly correlated (P < 0.0001). Receiver operator characteristic curve analysis demonstrated that the best cutoff for PAC after SLT was 5 ng/dl. Patients with aldosterone-producing adenoma displayed a smaller reduction of PAC compared with patients with bilateral adrenal hyperplasia; a PAC after SLT greater than 6 ng/dl identified all patients eventually diagnosed as having aldosterone-producing adenoma. Conclusions: This study demonstrates that the iv SLT is a reasonably good alternative to the more expensive and complex FST for the diagnosis of PA after a positive screening test.