Dual-reporting aldosterone by mass spectrometry and immunoassay in the seated saline suppression test may enhance subtype classification of patients with primary aldosteronism.

Immunoassay aldosterone measurements are frequently higher than liquid chromatography-tandem mass spectrometry (LC-MS/MS) results, potentially increasing the overdiagnosis of primary aldosteronism (PA) during the seated saline suppression test ​(SSST). This study determined the rate of concordance between LC-MS/MS and immunoassay aldosterone measurements following SSST and compared the adrenal vein sampling (AVS) lateralisation rates in patients with concordant and discordant SSST results. This retrospective analysis comprised 151 patients who underwent SSST in Western Australia and had dual-reported SSST aldosterone LC-MS/MS and immunoassay results, with 55 patients who proceeded to AVS studies. PA was excluded in 22.5% (34/151) of patients by a post-SSST immunoassay aldosterone result ​≤170 pmol/L plus an LC-MS/MS result ​<120 pmol/L, 32.5% (49/151) had PA confirmed by an immunoassay aldosterone result ​>170 pmol/L and an LC-MS/MS result ​>162 pmol/L, ​and 45.0% (68/151) had an immunoassay result ​>170 pmol/L, which was discordant with the LC-MS/MS result ​≤162 pmol/L. Comparable rates of AVS lateralisation of 82.1% (32/39) and 81.3% (13/16) were present in patients with concordant and discordant SSST results, respectively. In patients with lateralised AVS results, non-classical adrenal histopathology was found in 50.0% (8/16) of adrenalectomised patients with concordant SSST results compared with 88.9% (8/9) with discordant SSST results (p=0.088). Dual-reporting of post-SSST LC-MS/MS and immunoassay aldosterone results may offer additional diagnostic classification in patients being selected for AVS and may identify higher rates of micronodular variants of PA, although further investigation is required.