Definition The metyrapone test evaluates how the adrenal glands respond to adrenocorticotrophic hormone, or ACTH. ACTH is made in the pituitary gland and travels through the bloodstream to the adrenal glands. There it triggers the release of another hormone called cortisol.
Cortisol affects the breakdown and use of fats, carbohydrates, sodium, potassium, and protein. In this test, the medication metyrapone is given to a person to evaluate the ability of the adrenal gland to make cortisol.
Who is a candidate for the test? The metyrapone test may be done if a problem is suspected in a person's:
adrenal gland, such as a tumour or other factor that keeps the gland from working correctly
How is the test performed? Metyrapone is given in 4 doses over a 24-hour period, or sometimes as a single dose at 11 p.m. Metyrapone is given orally in tablet form. At 8 a.m., a blood sample is taken from a vein on the forearm or hand.
First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow. A fine needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle. It is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered to prevent bleeding . The blood sample is sent to a laboratory. There, cortisol and ACTH in the blood sample are measured.
What is involved in preparation for the test? Because metyrapone test preparation may vary, a person should ask his or her doctor for specific instructions.
What do the test results mean? When results of the metyrapone test are normal:
11-deoxycortisol, which is an enzyme that is made before cortisol, rises to more than 7 micrograms per decilitre of blood (mcg/dl)
cortisol is increased to less than 10 mcg/dl
the ACTH level rises higher than the level obtained from a baseline ACTH level.
Abnormal results may vary as follows:
No rise in the ACTH level may mean that the pituitary gland is not working normally. This is called hypopituitarism.
A great rise in 11-deoxycortisol is a sign of excessive tissue growth in the adrenal gland. Called adrenal hyperplasia, this condition causes the gland to enlarge.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Herane Last Updated: 21/03/2005 Contributors Potential conflict of interest information for reviewers available on request
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