Dexamethasone Suppression Test

Posted October 2, 2022 by Anusha ‐ 2 min read

The dexamethasone suppression test (DST) is used to assess adrenal gland function by measuring how cortisol levels change in response to oral doses or an injection of dexamethasone. It is typically used to diagnose Cushing's syndrome.

What is Dexamethasone

  • Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary gland to suppress the secretion of adrenocorticotropic hormone (ACTH).

  • Specifically, dexamethasone binds to glucocorticoid receptors in the anterior pituitary gland, which lie outside the blood-brain barrier, resulting in regulatory modulation.

Dexamethasone Suppression Test Procedures

There are several types of DST procedures:

  • Overnight DST - An oral dose of dexamethasone is given between 11pm and midnight, and the cortisol level is measured at 8 - 9am the next morning

  • Two-day DST - This involves giving an oral dose of dexamethasone at six-hourly intervals for 2 days, with the cortisol level measured 6 hours after the final dose was given

  • Intravenous DST

  • Dexamethasone-CRT test

Results interpretation of Dexamethasone Suppression Test

  • Low-dose and high-dose variations of the test exist.

  • The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone, and the levels of cortisol are measured to obtain the results.

  • A low dose of dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production.

  • A high dose of dexamethasone exerts negative feedback on pituitary neoplastic ACTH-producing cells (Cushing’s disease), but not on ectopic ACTH-producing cells or adrenal adenoma (Cushing’s syndrome).

  • A normal result is a decrease in cortisol levels upon administration of low-dose dexamethasone.
  • Results indicative of Cushing’s disease involve no change in cortisol on low-dose dexamethasone, but inhibition of cortisol on high-dose dexamethasone.
  • If the cortisol levels are unchanged by low- and high-dose dexamethasone, then other causes of Cushing’s syndrome must be considered with further work-up necessary.
  • After the high-dose dexamethasone, it may be possible to make further interpretations.
Is not suppressed by low or high dosesUndetectable or lowPrimary hypercortisolism is likely; Cushing’s syndrome, not disease (i.e., the hypercortisolism is not driven by ACTH
Is not suppressed by low doses, but is suppressed by high dosesNormal to elevated but not in hundredsCushing’s disease should be considered because the pituitary still retains some feedback control. A pituitary MRI would be needed to confirm.
Is not suppressed by high or low dosesElevated in hundredsEctopic ACTH syndrome is likely. If an adrenal tumor is not apparent, a chest CT and abdominal CT is indicated to rule out a different tumor secreting ACTH.
dexamethasone-suppression-test lab-tests lab-investigations investigations

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