[Diagnostic value of urinary free cortisol in the subclinical Cushing's syndrome in patients with adrenal incidentaloma].

Objective: To evaluate the efficacy of 24 h urinary free cortisol (24 h UFC) in the diagnosis of subclinical Cushing's syndrome (SCS), and explore the best diagnostic cut-off value. Methods: The clinical data of patients with adrenal incidentaloma in Chinese PLA General Hospital between January 2008 and December 2016 was retrospectively reviewed and analyzed. All SCS patients were diagnosed based on the current Cushing's syndrome (CS) guidelines and confirmed by histopathology and then treated as study group, and additional patients with non-functional adrenal adenoma (NFA) were enrolled as control group. ROC curve was used to evaluate efficacy of 24 h UFC and 24 h UFC to creatinine ratio (UFCCR), and explore their best cut-off values. Results: There were 161 patients with NFA, of which contained 84 males and 77 females, with a mean age of (51.02±10.49) years old. There were 88 patients with SCS, of which contained 26 males and 62 females, with a mean age of (51.74±10.29) years old. The 24 h UFC and UFCCR levels were significant higher in SCS group than those in NFA group[510 (363, 698) nmol vs 335 (209, 467) nmol for 24 h UFC, and 7.82(4.79, 12.13) ml vs 4.82(2.41, 6.57)ml for UFCCR, both P <0.05]. ROC analysis showed that the optimal cut-off for 24 h UFC was 480 nmol (AUC 0.716, 95% CI: 0.648-0.784, with a sensitivity of 58.0% and a specificity of 79.4%) and the optimal cut-off for UFCCR was 6.84 ml (AUC 0.729, 95% CI: 0.662-0.796, with a sensitivity of 59.1% and a specificity of 78.7%). Conclusions: The recommended cut-off points of 24 h UFC and UFCCR for diagnosing SCS in AI patients were 480 nmol and 6.84 ml, respectively.