The high-dose dexamethasone suppression test is for patients diagnosed with Cushing syndrome which is ACTH-dependent to determine whether the source of ACTH is the pituitary (Cushing disease) or an ectopic source (i.e. small cell lung cancer). A low dose of dexamethasone will fail to suppress an over stimulated adrenal, however high dose dexamethasone will suppress an overstimulated pituitary but fail to suppress an ectopic source of ACTH. 24-hour free urine cortisol is a collection of the total excreted cortisol in urine over a day. It is elevated in patients with Cushing syndrome due to increased production and elevated circulating levels. A corticotropin release hormone (CRH) test is used to differentiate between a pituitary tumor and an adrenal or ectopic tumor and is based on the premise that pituitary tumors are still responsive to CRH while ectopic and adrenal tumors are not.