Dexamethasone Suppression Test

Alternate Names

  • Prolonged/Rapid DST
  • Cortisol Suppression Test
  • ACTH Suppression Test

DST measures cortisol (steroid) levels following the administration of the medication dexamethasone, and is used to diagnose diseases that affect adrenal gland function. The adrenal glands normally release cortisol and 17-hydroxycorticosteroid (17-OCHS) after stimulation by ACTH released by the pituitary gland.

Dexamethasone will normally decrease the amount of ACTH produced by the body. As blood levels of cortisol increase, levels of ACTH will decrease and vice versa. DST can be very specific for the cause of illness. Abnormal levels of ACTH are seen in people with cancer of the adrenal glands, malignant cancers that secrete ACTH, Cushing's syndrome, an over-active thyroid gland, or depression.

The Rapid DST test takes approximately 24 hours and is used to quickly rule out the presence of Cushing's syndrome. The Prolonged DST Test takes six days, is more accurate than the Rapid Test, and can be done as an outpatient.


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