Urinary cortisol level in exclusion autonomous cortisol secretion in the patient of primary aldosteronism

Abstract Background Serum cortisol level after 1-mg overnight dexamethasone suppression test (1-mg DST) below 1.8 ug/dL was a diagnostic criterion for having autonomous cortisol secretion (ACS), whether the cut-off point in 24-hour urine-free cortisol (24-h UFC) for the patient suspecting with primary aldosteronism (PA) concomitant ACS is unclear. Methods This prospective observational study enrolled 274 patients diagnosed with PA from January 2017 to January 2020 (male, 42.3%; mean age, 55.9 ± 11.7 years). Serum cortisol level after 1 mg DST over 1.8 ug/dL was a diagnostic criterion for ACS, confirmed with a second repeated test. Results Of the 274 PA patients, 74 patients (27%) with PA had concomitant ACS while the other 200 patients were not. Logistic regression analysis showed patients with PA concomitant ACS were associated with higher 24-h UFC (OR, 1.91 [95% CI, 1.06–3.41], P=0.03), older age (OR, 1.04 [95% CI, 1.01–1.07], P=0.008), and diabetes mellitus (OR, 2.4 [95% CI, 1.12–5.12], P=0.025). The generalized additive model (GAM) for urinary cortisol and ACS showed the 24-h UFC above 36 μg, concurrent with the positive predictive value of 32.6% and negative predictive value of 77.9% could be a factor predicting a higher possibility of ACS. Conclusions More than a quarter of PA patients concomitant ACS. Our study suggested the 24-h UFC less than 36 μg as a cut-off point in exclusion of the patient with PA concomitant ACS. Additionally, older age and diabetes mellitus were also risk factors for predicting patients with PA concomitant ACS.