Re-evaluation of the optimal cutoff of saline infusion test in the diagnosis of primary aldosteronism

Objective To assess the diagnostic value of saline infusion test (SIT) and its optimal cutoff in the diagnosis of primary aldosteronism (PA), and to analyze whether the dietary salt intake affects the SIT accuracy. Methods This is a prospective study. All 236 patients with a high risk for PA underwent the screening test, SIT and the fludrocortisone suppression test (FST) in separate days. The diagnosis of PA was established according to the FST criteria. According to the 24 h urinary sodium level, the patients were divided into low salt, normal salt, and high salt groups respectively, and the effect of salt intake on SIT was analyzed. Receiver operating characteristic (ROC) analysis was performed to compare the diagnostic accuracies. Results Finally, in 236 patients with high risk for PA, 134 patients with PA and 102 patients with essential hypertension (EH) were diagnosed. Using post-test plasma aldosterone concentration (PAC) for diagnosis, the area under the ROC curve (AUCROC) of the SIT was 0.974 (0.957, 0.991), which was significantly higher than that of the post-test plasma aldosterone to renin ratio (ARR) [0.900 (0.862, 0.938)] and that of the PAC suppression percentage [0.752 (0.690, 0.813)] (both P 0.05). Conclusion SIT is reliable for the diagnosis of PA. PAC post-SIT more than 8.0 ng/dl is recommended to confirm PA. (Chin J Endocrinol Metab, 2018, 34: 460-465) Key words: Primary aldosteronism; Saline infusion test; Sensitivity; Specificity