[Practical application of the captopril challenge test for diagnosing primary aldosteronism]

Objective: To investigate the diagnostic efficacy of the captopril challenge test (CCT) for primary aldosteronism (PA). Methods: Hypertensive patients suspected of having PA who visited the First Affiliated Hospital of Sun Yat-sen University from July to December 2021 were prospectively collected. The patients were divided into an essential hypertension (EH) group and a PA group based on etiology. All patients completed the CCT, and their plasma aldosterone concentration (PAC) was detected using both chemiluminescence immunoassay (CLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The area under the receiver operating characteristic curve (AUC) was used to evaluate the diagnostic efficacy of each parameter, with the maximum Youden index selected as the cut-off value. The DeLong test was applied to compare the differences in AUC among various diagnostic parameters. Results: A total of 88 patients were included, consisting of 45 in the EH group and 43 in the PA group. Patients in the PA group were older than those in the EH group [(52.1±10.5) vs (47.6±13.5) years]. The PA group had lower serum potassium [3.5 (3.1, 4.0) vs 3.9 (3.7, 4.1) mmol/L] and direct renin concentration (DRC) [3.0 (2.0, 6.0) vs 14.0 (9.0, 22.0) ng/L], but higher serum sodium [143.0 (140.0, 145.0) vs 141.0 (139.0, 142.0) mmol/L], PAC [34.9 (26.6, 69.1) vs 23.9 (17.2, 29.8) ng/dl] and plasma aldosterone-to-renin ratio (ARR) [9.8 (5.0, 44.4) vs 1.6 (1.0, 2.7) (ng·dl^-1)/(ng·L^-1)] (all P<0.05). Among all parameters for diagnosing PA, the top 3 indicators with the largest AUC values were ARR at 1 h post-CCT (PAC measured by CLIA) [0.953(95%CI:0.886-0.987)], ARR at 2 h post-CCT (PAC measured by CLIA) [0.970(95%CI:0.909-0.994)], and ARR at 2 h post-CCT (PAC measured by LC-MS/MS) [0.952(95%CI: 0.884-0.986)]. Pairwise comparisons of the AUCs among these 3 indicators showed no statistically significant differences (all P>0.05), and their optimal cut-off values were 2.6, 2.5, and 1.6 (ng·dl^-1)/(ng·L^-1), respectively. Conclusion: The ARR at 1 h post-CCT may serve as a simpler, more convenient, and accurate diagnostic indicator for PA.