Dexamethasone is a steroid that is used in a variety of circumstances. It is a powerful corticosteroid that is many more times powerful than hydrocortisone, prednisone, and predisalone. As a drug it is used as any corticosteroid is - to suppress inflammatory response when required. Dexamethasone works by disrupting a very specific system in the body which controls the stress response. This system is the hypothalamic-pituitary-adrenal or HPA axis. When dexamethasone is administered, it should reduce the amount of a stress hormone secreted called cortisol. This is a useful facet that is used in a test called the dexamethasone suppression test.
The dexamethasone suppression test is a test that is used to understand hypercortisol states. This is a condition called Cushing’s syndrome and usually indicates some kind of tumor. The test is also used to check for the integrity of the HPA axis in mood disorders.
The test is performed by taking a sample of blood and testing for levels of cortisol and ACTH after administering dexamethasone. The long dexamethasone suppression test is performed to check the immediate reaction of administering the drug on the HPA axis. Normally, the HPA axis uses a negative feedback system to control it. The hypothalamus on sensing the need to send the body into a stress situation will stimulate the pituitary gland to secrete a hormone called ACTH or adrenocorticotropin. ACTH then stimulates the adrenal glands to immediately synthesize cortisol from cholesterol. This also causes norepinephrine and cortisol levels to rise, which then go back to the brain and suppress further creation of ACTH - thus rendering the body back in balance.
There is no preparation required for this but you must ensure that you do not take any painkiller medication before this test. If you are going to undergo an overnight dexamethasone suppression test, then you might need to prepare for an overnight stay at your medical center. Interpretation of the results is something that you must understand. Low ACTH levels but cortisol levels being high irrespective of dexamethasone dosage indicates an adrenal tumor. Normal and elevated ACTH, high cortisol despite dexamethasone high or low doses indicates that there is a tumor somewhere else in the body secreting ACTH. Normal and elevated ACTH but cortisol levels that only reduce with high doses of dexamethasone indicate a pituitary tumor. A normal result occurs when the body responds by reducing the amount of cortisol produced when a low dose of dexamethasone is administered.