To evaluate the diagnostic value of different doses (1 mg and 2 mg) of overnight dexamethasone suppression test (ODST) in the screening of Cushing's syndrome, and to explore the optimal screening drug dose and cut point; in order to increase the detection rate of this disease in clinical work, and to reduce the adverse reactions that the drug may cause to human body.

A retrospective analysis was performed on the clinical data of 96 patients with Cushing's syndrome (the Cushing's syndrome group) and 61 clinical suspected cases (the non-Cushing's syndrome group) admitted to the Department of Endocrinology and Metabolism of the Provincial Hospital Affiliated to Shandong University from Jan. 2000 to Dec. 2017. Under the same diagnostic cut-point, the degree of serum cortisol inhibition, diagnostic sensitivity, specificity, and false-positive rate after different dose tests were compared. And at the same dose of drug, the sensitivity and specificity of different diagnostic cut-points in disease screening were compared.

In the 1-mg ODST, the cortisol inhibition rate was 17.9% in the Cushing's syndrome group and 78.7% in non-Cushing's syndrome group. And in the 2-mg ODST, the cortisol inhibition rate was 24.2% in the Cushing's syndrome group, compared with 87.2% in the non-Cushing syndrome group. When taking the serum cortisol at 8:00 on the day of the test as basal value and taking serum cortisol < 50 nmol/L (1.8 μg/dl) on the following day as the diagnosis cut-off point for Cushing's syndrome, the diagnostic sensitivity and specificity for the 1-mg ODST were 100% and 42.8%, respectively; and that for the 2-mg ODST were 100%, and 69.7%, respectively. If taking serum cortisol < 138 nmol/L (5 μg/dl) on the following day as the diagnosis cut-off point, the sensitivity and specificity of 1-mg ODST in the diagnosis of Cushing's syndrome are 100% and 85.7%, respectively; and that for the 2-mg ODST were 100% and 93.9%, respectively. In the screening of Cushing's syndrome, 2-mg ODST was more accurately than 1-mg ODST at the same diagnostic site. And at the same dose, taking serum cortisol at 8:00 on the following day was <138 nmol/L (5 μg/L). Dl) as the diagnostic cut point brought no significant difference in diagnostic sensitivity, but could give higher specificity and more accurate diagnosis rate.

In the screening process of Cushing's syndrome, when taking the serum cortisol at 8:00 on the following day <138 nmol/L (5 μg/dl) as the diagnosis point of Cushing syndrome, the diagnosis accuracy rate of 2-mg ODST improved significantly with more accurate diagnose result, which is worth popularizing and applying in practice.