The dexamethasone suppression test (DST) is used to assess

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...

function by measuring how cortisol levels change in response to oral doses or an injection of

dexamethasone Dexamethasone is a glucocorticoid medication used to treat rheumatic problems, a number of skin diseases, severe allergies, asthma, chronic obstructive lung disease, croup, brain swelling, eye pain following eye surgery, superior vena ...

. It is typically used to diagnose

Cushing's syndrome Cushing's syndrome is a collection of signs and symptoms due to prolonged exposure to glucocorticoids such as cortisol. Signs and symptoms may include high blood pressure, abdominal obesity but with thin arms and legs, reddish stretch marks, a ...

. The DST was historically used for diagnosing depression, but by 1988 it was considered to be "at best, severely limited in its clinical ability" for this purpose.

Physiology

Dexamethasone is an exogenous steroid that provides negative feedback to the

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...

to suppress the secretion of

adrenocorticotropic hormone Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important c ...

(ACTH). Specifically, dexamethasone binds to

glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every verteb ...

receptors in the anterior pituitary gland, which lie outside the blood–brain barrier, resulting in regulatory modulation.

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

Interpretation

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).

Dose

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. †ACTH as measured prior to dosing of dexamethasone Equivocal results should be followed by a

corticotropin-releasing hormone Corticotropin-releasing hormone (CRH) (also known as corticotropin-releasing factor (CRF) or corticoliberin; corticotropin may also be spelled corticotrophin) is a peptide hormone involved in stress responses. It is a releasing hormone that bel ...

stimulation test, with inferior petrosal sinus sampling.

References

* Theodore C. Friedman, M.D., Ph.D. Professor of Medicine-UCLA Chairman, Department of Internal Medicine Charles R. Drew University (2013)

{{DEFAULTSORT:Dexamethasone Suppression Test Endocrine procedures Dynamic endocrine function tests