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 Cushings syndrome. 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 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. 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 (Cushings disease), but not on ectopic ACTH-producing cells or adrenal adenoma (Cushings syndrome).
Prognosis
No serious long-term effects are known for this disease, but preliminary evidence suggests, if such symptoms do occur, they are less severe than those associated with Lyme disease. See also
Borrelia
Zoonosis

References
External links

Southern Tick-Associated Rash Illness (STARI) Home Page Centers for Disease Control
STARI Fact Sheet Florida Department of Health
Southern Tick-Associated Rash Illness (STARI) SCWDS Briefs, January 2003, Vol.18, No.4