Abstract:

Objective To evaluate the accuracy of 2 mg dexamethasone suppression test (DST) with serum cortisol or inhibition rate as cut-off points in diagnosis of Cushing's syndrome. Methods The clinical data of 163 patients with Cushing's syndrome confirmed by pathological examinations after operation were collected. The baseline serum cortisol levels at 8:00 and serum cortisol levels after 2 mg DST were recorded, and inhibition rates were calculated. Serum cortisol level and inhibition rate were served as cut-off points for diagnosis of Cushing's syndrome in 2 mg DST, and coincidence with pathological diagnosis was analysed. Results Pathological examinations after operation confirmed that there were 94 cases of Cushing disease, 63 cases of corticosuprarenaloma and 6 cases of ectopic adrenocorticotropic hormone (ACTH) syndrome among 163 cases of Cushing syndrome. With serum cortisol >5  g/dL after 2 mg DST as cut-off point, 88 cases of Cushing disease, 63 cases of corticosuprarenaloma and 6 cases of ectopic ACTH syndrome were diagnosed, and coincidence with pathological diagnosis was 96.3%. With inhibition rate <50% after 2 mg DST as cut-off point, 68 cases of Cushing disease, 63 cases of corticosuprarenaloma and 6 cases of ectopic ACTH syndrome were diagnosed, and coincidence with pathological diagnosis was 84.0%. Conclusion Compared with inhibition rate <50% after 2 mg DST as cut-off point, serum cortisol>5 g/dL after 2 mg DST as cut-off point may yield higher accuracy in diagnosis of Cushing's sydrome.

Key words: Cushing´s syndrome, 2 mg dexamethasone suppression test, serum cortisol, suppression rate