SEATED SALINE SUPPRESSION TESTING IS COMPARABLE TO CAPTOPRIL CHALLENGE TEST FOR THE DIAGNOSIS OF PRIMARY ALDOSTERONISM: A PROSPECTIVE STUDY

Abstract Background Saline suppression testing (SST) and captopril challenge test (CCT) are commonly used confirmatory tests for primary aldosteronism (PA). Seated SST (SSST) is reported to be superior to recumbent SST (RSST). Whether SSST is better than CCT remains unclear. Objective To compare the diagnostic accuracy of SSST and CCT in a prospective study. Methods Hypertensive patients with high risk of PA were consecutively included. Patients with aldosterone-renin ratio≥1.0 ng·dl-1/μIU·ml-1 were asked to complete SSST, CCT and fludrocortisone suppression test (FST). Using FST as the reference standard (plasma aldosterone concentration [PAC] post-FST ≥6.0 ng·dl-1), area under the receiver-operator characteristic curves (AUC), sensitivity and specificity of SSST and CCT were calculated, and multiple regression analyses were conducted to identify potential factors for false diagnosis. Results A total of 196 patients diagnosed as PA and 73 as essential hypertension completed the study. Using PAC post-SSST and PAC post-CCT to confirm PA, SSST and CCT had comparable AUCs (AUCSSST 0.87 [95%CI 0.82 to 0.91] vs. AUCCCT 0.88 [0.83,0.95], P=0.646). Setting PAC post-SSST and post-CCT at 8.5 ng·dl-1 and 11 ng·dl-1, respectively, the sensitivity and specificity of SSST [0.72(0.65,0.78) and 0.86(0.76,0.93)] and CCT [0.73(0.67,0.80) and 0.85(0.75,0.92)] were not significantly different. In the multiple regression analyses, 1SD increment of sodium intake resulted in 40% lower risk of false diagnosis in SSST. Conclusions SSST and CCT have comparable diagnostic accuracy. Insufficient sodium intake decreases the diagnostic efficiency of SSST but not CCT. Since the CCT is simpler and cheaper, it is preferable to the SSST.