Dexamethasone suppression test
Alternative names:
ACTH suppression test; cortisol suppression test; DST
Normal values:
low dose: less than 50% reduction of plasma cortisol and 17-hydroxycorticosteroid (17-OCHS)
high dose: more than 50% reduction of plasma cortisol and 17-OCHS
What abnormal results mean:
In Cushing's syndrome related to bilateral adrenal hyperplasia, the pituitary gland is reset upward and responds only to high plasma levels of cortisol (or dexamethasone). In Cushing's syndrome related to adrenal adenoma (tumor) or cancer (which acts autonomously), cortisol secretion continues in spite of a decrease in ACTH. A similar situation is seen when Cushing's syndrome is caused by an ectopic ACTH-producing tumor.
Cushing's syndrome related to bilateral adrenal hyperplasia - low dose: no change
- high dose: > 50% reduction of plasma cortisol and 17-OCHS
Cushing's syndrome caused by adrenal tumor - low dose: no change
- high dose: no change
Cushing's syndrome related to ectopic ACTH-producing tumor - low dose: no change
- high dose: no change
Additional conditions under which the test may be performed:
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