[Establishing LC-MS/MS-based cutoffs for the confirmatory testing for primary aldosteronism: a prospective multi-center study].

Objective: To evaluate the diagnostic utility of confirmatory tests [captopril challenge test (CTT) and seated saline infusion test (SIT)] for primary aldosteronism (PA) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and establish optimized diagnostic cutoffs. Methods: This prospective multicenter diagnostic trial enrolled patients at high risk for PA from seven tertiary clinical centers in China between April 2023 and December 2024. All participants underwent aldosterone-to-renin ratio (ARR) screening, the CCT, and the seated SIT. Plasma aldosterone concentrations (PACs) and plasma renin levels were measured via LC-MS/MS and chemiluminescence immunoassay (CLIA). PA diagnosis was defined as a CLIA-based post-SIT PAC ≥8.5 ng/dl (235.8 pmol/L) combined with an upright plasma renin concentration of <15 mU/L. Receiver operating characteristic (ROC) curves based on LC-MS/MS data from the CCT and the SIT were plotted to evaluate diagnostic performance. The DeLong test was employed for area under the ROC curve (AUC) comparisons among subgroups. Optimal diagnostic cutoffs for PA were determined based on sensitivity and specificity. Results: The study included 117 patients diagnosed with PA [age: (48±10) years; 58 (49.57%) males] and 354 patients diagnosed with essential hypertension [age: (45±12) years; 207 (58.47%) males]. Two hours post-CCT using mass spectrometry, the AUCs for the ARR and PAC were 0.858 and 0.837, respectively, both superior to PAC suppression percentage (AUC=0.718, both P<0.001). Additionally, the diagnostic efficacy of ARR was significantly better than that of plasma renin activity (PRA; AUC=0.784, P<0.001). At a diagnostic cutoff of PAC ≥5.7 ng/dl (158.1 pmol/L) or ARR ≥9.3 (ng/dl)/(ng·ml⁻¹·h⁻¹), sensitivity was 61% and specificity was 85%. For the seated SIT using mass spectrometry, the AUCs for the ARR and PAC were 0.828 and 0.852, respectively, significantly better than PRA (AUC=0.680, both P<0.001). At a PAC cutoff of ≥5.0 ng/dl (138.7 pmol/L), sensitivity was 68% and specificity was 85%, while an ARR cutoff of ≥ 19.0 (ng/dl)/(ng·ml⁻¹·h⁻¹) yielded a sensitivity of 64% and a specificity of 85%. Conclusions: Both the CCT and the SIT, based on LC-MS/MS, demonstrated excellent diagnostic performance. The recommended optimal cutoff for the ARR 2 hours post-CCT was 9.3 (ng/dl)/(ng·ml⁻¹·h⁻¹), while that for the PAC was 5.7 ng/dl. For the seated SIT, the optimal ARR cutoff was 19.0 (ng/dl)/(ng·ml⁻¹·h⁻¹) and the optimal PAC cutoff was 5.0 ng/dl.