Sample: Serum sample 8 hrs after dexamethasone adninistration
Range: Cortisol (a.m.) levels drop to very low values in healthy individuals
Remarks: Administration of Dexamethasone (a synthetic glucocorticoid that is 64 times more potent than cortisol) suppresses the release of ACTH by negative feedback in patients with a normal hypothalamic-pituitary-adrenal axis (Cushings disease). As a result, the cortisol (a.m.) levels decrease to very low levels in healthy individuals. Patients with hypercortisolism lose normal negative feedback control and they have higher cortisol (a.m.) levels after dexamethasone administration.