Urine Free Cortisol in the High-Dose Dexamethasone Suppression Test for the Differential Diagnosis of the Cushing Syndrome

In the high-dose dexamethasone suppression test, the degree of suppression of urine free cortisol used for the diagnosis of pituitary disease is greater than that traditionally used for 17-hydroxysteroid excretion. The diagnostic performance of the test is improved by measuring both urine free cortisol and 17-hydroxysteroid excretion and by requiring greater suppression of both steroids.