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Comparison of Confirmatory Tests for the Diagnosis of Primary Aldosteronism

Division of Internal Medicine and Hypertension (P.M., A.M., F.V.), University of Torino, 10133 Torino, Italy; Division of Internal Medicine 3 (F.F.), University of Padova, 35128 Padova, Italy; Division of Internal Medicine (G.R.), Reggio Emilia Hospital, 42100 Reggio Emilia, Italy; Division of Internal Medicine B (F.P.), University of Verona, 37134 Verona, Italy; Division of Endocrinology (C.F., L.Mo.), P. Universitad Catolica de Chile, 114D Santiago, Chile; and Division of Endocrinology and Metabolism (L.Ma., F.V., M.M.), University of Torino, 10126 Torino, Italy

Address all correspondence and requests for reprints to: Paolo Mulatero, M.D., Centro Ipertensione Ospedale San Vito, Strada San Vito 34, 10133, Torino, Italy. E-mail: paolo.mulatero{at}libero.it.

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.

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