| Dexamethasone suppression test | |
|---|---|
 | |
| Purpose | assess adrenal gland function |
Thedexamethasone suppression test (DST) is used to assessadrenal gland function by measuring howcortisol levels change in response to oral doses or an injection ofdexamethasone.[1] It is typically used to diagnoseCushing's 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.[2]
Dexamethasone is an exogenous steroid that provides negative feedback to thepituitary gland to suppress the secretion ofadrenocorticotropic hormone (ACTH). Specifically, dexamethasone binds toglucocorticoid receptors in the anterior pituitary gland, which lie outside theblood–brain barrier, resulting in regulatory modulation.[3]
There are several types of DST procedures:[1]
Low-dose and high-dose variations of the test exist.[4] 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.[5]
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).[citation needed]
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.[6]
| Cortisol | ACTH† | Interpretation |
|---|---|---|
| is not suppressed by low or high doses | Undetectable or low | Primary hypercortisolism is likely;Cushing's syndrome, not disease (i.e., the hypercortisolism is not driven by ACTH hypersecretion) |
| is not suppressed by low doses, but is suppressed by high doses | Normal to elevated but not in hundreds | Cushing'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 doses | Elevated in hundreds | Ectopic 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. |
†ACTH as measured prior to dosing of dexamethasone[7]
Equivocal results should be followed by acorticotropin-releasing hormonestimulation test, withinferior petrosal sinus sampling.