Comparison of confirmatory tests for the diagnosis of primary aldosteronism

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.

Our objective was to compare the specificity of SLT with FST for the diagnosis of PA.

The study included 100 hypertensive patients referred to hypertension units with suspected PA after the screening test.

All patients underwent FST and SLT.

We assessed plasma aldosterone concentrations (PAC) before and after FST and SLT.

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.

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.