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Dexamethasone suppression test

Alternative Names: DST; ACTH suppression test; Cortisol suppression test Normal Values: Low Dose: Overnight: 8 a.m. plasma cortisol < 5 mcg/dl Standard: Urinary free cortisol on day 3 < 10 mcg/day Text Continues Below High Dose: Overnight: > 50 % reduction in plasma cortisol Standard: > 90% reduction in urinary free cortisol Normal value ranges may vary slightly among different laboratories. What abnormal results mean: If there is not a normal response on the low-dose test, abnormal secretion of cortisol is likely (Cushing's Syndrome). This could be a result of a cortisol-producing adrenal tumor, a pituitary tumor that produces ACTH, or a tumor in the body that inappropriately produces ACTH. The high-dose test can help distinguish a pituitary cause (Cushing's Disease) from the others. Cushing's syndrome caused by adrenal tumor Low dose: no change High dose: no change Cushing's syndrome related to ectopic ACTH-producing tumor Low dose: no change High dose: no change Cushing's Syndrome caused by pituitary tumor (Cushing's Disease) Low dose: no change High dose: normal suppression

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