The saline infusion test with mass spectrometric measurements of aldosterone to confirm primary aldosteronism.

Objective: Confirmation of primary aldosteronism with the saline infusion test requires accurate measurements of plasma aldosterone, which is best achieved by mass spectrometry. Diagnostic performance, appropriate cut-offs and intra-patient variability of the test remain inadequately defined. The objective of this prospective multicenter cohort study was to address these limitations.

Methods: Primary aldosteronism was confirmed and excluded using alternative criteria to confirmatory tests in 138 and 282 respective patients with suspected disease. Those criteria were not satisfied in 89 patients. Diagnostic performance of the saline infusion test and optimal cut-offs were determined from receiver operating characteristic curves. Intra-patient variability was determined in 57 patients.

Results: Analysis of receiver operating characteristic curves indicated an area under the curve of 0.964 and a cut-off of 169 pmol/l for posttest aldosterone concentrations that provided 97% sensitivity and 89% specificity. A cut-off of 255 pmol/l enabled improved specificity of 95% at a sensitivity of 75%. Among the 57 patients in whom the saline infusion test was repeated, 15 (26%) had posttest aldosterone concentrations that were discordant using the 169 pmol/l cut-off. Eighty percent of the discordant results were from a single center. With exclusion of that center, which did not minimize ambulation during saline infusion, the area under the curve increased to 0.985 and an optimal cut-off of 169 pmol/l provided 96% specificity and sensitivity.

Conclusion: The seated saline infusion test with mass spectrometric measurements of aldosterone and the cut-offs documented here provides a useful confirmatory test, although this requires adherence to standard-operating procedures.