Dexamethasone suppression test
|Dexamethasone suppression test|
The dexamethasone suppression test (DST) is a blood test that assesses adrenal gland function by measuring how cortisol levels change in response to an injection of dexamethasone. It is typically used to diagnose Cushing's syndrome. It may also play a role in diagnosing depression, but this application is still considered experimental.
Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary to suppress the secretion of ACTH. Specifically, dexamethasone binds to glucocorticoid receptors in the pituitary gland, which lies outside the blood brain barrier, resulting in regulatory modulation.
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 dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production. A high dose dexamethasone exerts negative feedback on pituitary ACTH-producing cells but not on ectopic ACTH-producing cells or adrenal adenoma.
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.
|Undetectable or low||is not suppressed by high or low doses.||Primary Hypercortisolism is likely.|
|Elevated in hundreds||is not suppressed by high or low doses||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.|
|Normal to elevated but not in hundreds||is not suppressed by low doses, but is suppressed by high doses||Cushing's disease should be considered. This is because the pituitary still retains some feedback control. A pituitary MRI would be needed to confirm.|
†ACTH as measured prior to dosing of dexamethasone
- Medline Plus "Dexamethasone suppression test"
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