The dexamethasone inhibition test is a primary test method for suspected hypercortisolism (hypercortisolism).A distinction is made between a dexamethasone short test and a long test.If a clear result cannot be obtained by the dexamethasone short test, the dexamethasone long test is also performed.
Dexamethasone is one of the synthetic glucocorticoids and is used therapeutically for many different diseases.
The procedure – dexamethasone short test
Before the dexamethasone is administered, a blood sample is taken in the morning on an empty stomach (8 am) to determine the serum cortisol level. In the late evening (11 pm), a dose of dexamethasone (2 mg) is administered. The next morning, again fasting (8 am), blood sampling for cortisol determination.
The procedure – dexamethasone long-term test
Before the dexamethasone is administered, a blood draw is performed in the morning fasting (8 am) to determine the serum cortisol level. In the late evening (11 pm) of the first day, a dose of dexamethasone (2 mg) is administered. The next morning, again fasting (8 a.m.), blood is drawn for cortisol determination. This procedure is repeated for another two days, with 4 and 6 mg of dexamethasone, respectively. A final blood draw is performed on the morning of the fourth day.
Indications
- Suspected hypercortisolism
- Dexamethasone long test can distinguish between a pituitary (affecting the pituitary gland) and adrenal (affecting the adrenal cortex) cause
Interpretation – dexamethasone short test
Normally, serum cortisol drops to < 3 μg/dl on day two.If cortisol does not drop sufficiently, hypercortisolism is suspected – Adrenocortical adenoma – benign tumor of the adrenal cortex- Adrenocortical carcinoma – malignant tumor of the adrenal cortex.
Interpretation- dexamethasone long test
If the cortisol level does not decrease until the fourth day (after 4 mg of dexamethasone), pituitary hypercortisolism is almost certainly present.If no decrease in cortisol occurs even after the third suppressive dose of 8 mg of dexamethasone, adrenal hypercortisolism is probably present.
