Dexamethasone is an active substance from the glucocorticoid group.Dexamethasone has a small amount of mineralocorticoid properties. It is among the potent glucocorticoids.
The dexamethasone long test(high-dose test) describes a test procedure (dexamethasone inhibition test;dexamethasone suppression test) to determine whether there is a decrease in endogenous cortisol concentration after glucocorticoid ingestion.
Procedure
Material Needed
- Blood serum
Preparation of the patient
The test lasts four days and is started on Monday or Tuesday.
- At 8 a.m., fasting blood draw to determine basal cortisol levels.
- At 11 p.m., intake of 2 mg dexamethasone orally
- At 8 am of the second day fasting blood sampling to determine the first suppression value.
- At 11 p.m., intake of 4 mg of dexamethasone orally
- At 8 am of the third day fasting blood sampling to determine the second suppression value.
- At 11 p.m., intake of 6 mg of dexamethasone orally
- At 8 a.m. on the fourth day, fasting blood collection to determine the third suppression value
Confounding factors
- Fasting blood collection
Normal values
| Normal value basal | 4-22 μg/dl |
| Normal value from second day | <3 μg/dl |
A regular drop in cortisol concentration excludes Cushing’s syndrome 99% of the time.
Indications
- When hypercortisolism (excess cortisol) is detected, to clarify the etiology (cause) – pituitary (pituitary gland) or adrenal (adrenal gland) hypercortisolism.
Interpretation
Interpretation – delayed decrease in cortisol concentration (3rd suppression value).
- Cushing’s syndrome, hypothalamic-pituitary related – pituitary hypercortisolism caused by a dysfunction in the diencephalon/pituitary region.
Interpretation – insufficient drop in cortisol concentration (3rd suppression value).
- Cushing’s syndrome, adrenal related – adrenal hypercortisolism caused by a neoplasm such as adenoma/carcinoma of the adrenal cortex.
- Ectopic hypercortisolism – presence of a neoplasm that produces ACTH.
