Objective: Primary aldosteronism (PA) is the commonest cause of endocrine hypertension ranging from 4.6%-16.6% according to the diagnostic tests employed. The aim of this study was to compare the traditional saline infusion test (SIT) with the modified post-dexamethasone SIT (DSIT) by applying both tests on the same subjects. Methods: We studied 68 patients (72% hypertensives) with single adrenal adenoma and 55 normotensive controls, with normal adrenal imaging. Serum cortisol, aldosterone and plasma renin concentration (PRC) were measured and the aldosterone-to-renin ratio (ARR) was calculated. Using the mean+2SD values from the controls, we defined the upper normal limits (UNL) for cortisol, aldosterone and PRC for both the SIT and DSIT. Results: In the controls, the post-DSIT aldosterone levels and the ARR were approximately 2-fold and 3-fold lower respectively than the corresponding post-SIT values (all p=0.001) leading to lower cut-offs of aldosterone suppression. Applying these cut-offs to patients with adrenal adenomas, the prevalence of PA was 13.2% following the SIT and 29.4% following the DSIT, respectively. In addition, 54.5% of patients with PA had concomitant autonomous cortisol secretion. Targeted treatment of PA resulted in resolution of hypertension and restoration of normal secretory aldosterone dynamics. Conclusions: The DSIT improves the diagnostic accuracy of PA, allowing for the detection of milder forms of PA in patients with adrenal adenomas. This is of particular importance as such patients may be at an increased risk for developing cardiovascular and renal morbidity that could be enhanced in the presence of concomitant autonomous cortisol secretion.

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