Rapid dexamethasone suppression test for Cushing's syndrome

The practical application of the overnight dexamethasone suppression test for preliminary screening for Cushing's syndrome can be extended by the utilization of a steroid-creatinine ratio calculated from urine collected in a five-hour period, ie, 7:00 AM to 12:00 noon. The use of the urine ratio obviates the necessity of a quantitatively accurate urine collection, and hence makes it a more feasible outpatient screening procedure. A ratio of less than 4 makes the diagnosis of Cushing's syndrome highly unlikely, whereas a ratio greater than 4 requires that further studies be performed to establish a definitive diagnosis of Cushing's syndrome.