SUN-469 Practical Application Of The Captopril Challenge Test For Diagnosing Primary Aldosteronism

Abstract Disclosure: F. Lai: None. W. Chen: None. A. Vaidya: None. S. Yu: None. C. Xu: None. H. Xiao: None. Y. Li: None. X. Cao: None. Objective: The interpretation of captopril challenge test (CCT) results remains debated. We aimed to identify the optimal CCT diagnostic threshold for primary aldosteronism (PA). Methods: A total of 88 patients at high risk for PA underwent CCT involving the administration of 50-mg captopril followed by measurements at 1-h and 2-h post captopril. Plasma aldosterone concentration (PAC) during CCT was measured by both chemiluminescence immunoassay (CLIA) and liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results: Among the various diagnostic thresholds assessed, the plasma aldosterone-to-renin ratio (ARR) 2-h post CCT presented the highest diagnostic efficiency regardless of whether PAC was measured via CLIA or LC-MS/MS. The area under the receiver operating characteristic curves (AUC) for 2-h post CCT were 0.970 (95% confidence interval [CI] 0.909 – 0.994) for PAC measured with CLIA and 0.952 (95% CI 0.884 – 0.986) for PAC measured with LC-MS/MS, which were significantly higher than the AUCs using the absolute value of PAC,and the percent decline of PAC or ARR after captopril (P < 0.05). However, the ARR 1-h post CCT (AUC = 0.953 [95% CI 0.886 – 0.987]) displayed similar diagnostic accuracy when compared to the ARR 2-h post CCT for PAC measured with CLIA. The optimal 1-h and 2-h post CCT diagnostic thresholds for ARR when PAC was measured via CLIA were 2.6 and 2.5, respectively. Conclusions: These findings indicated that the CCT can be performed and interpreted with high accuracy using CLIA assays for PAC measurement and by performing only a 1-h post CCT measurement. Presentation: Sunday, July 13, 2025