Metyrapone test

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Metyrapone test measures the ability of the pituitary gland to secrete ACTH in response to decreased serum cortisol.

There are two different types of metyrapone tests. The first is an overnight test. A single dose of metyrapone is given at 11 p.m. and blood is drawn at 8 a.m. for measurement of serum cortisol, ACTH, and another hormone called 11-deoxycortisol.

In the second form of the test, metyrapone is given 6 times a day for 24 hours and then a 24-hour urine sample is collected for measurement of 17-OHCS  (a metabolic product of cortisol). Blood samples for serum cortisol, ACTH, and 11-deoxycortisol may also be drawn.

The health care provider may advise you to temporarily discontinue drugs that may affect the test (for example, rifampin, phenobarbital, phenytoin). These drugs may have to be stopped for several weeks prior to the test. Other drugs that can affect metyrapone test measurements include chlorpromazine and corticosteroids. Birth control pills and other estrogen-containing medications can also cause false-positive results.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

The test is used to determine whether the pituitary gland is functioning properly. Metyrapone inhibits an enzyme (steroid 11-beta hydroxylase) that converts 11-deoxycortisol to cortisol. The resulting fall in serum cortisol levels normally stimulates the pituitary to secrete ACTH, which then attempts to stimulate the adrenal cortex to make cortisol. Since the enzyme is inhibited, 11-deoxycortisol builds up in the blood and urine.

Review Date: 03/03/2006
Reviewed By: David Juan, MD, Specializing in Endocrinology Issues, Good Hand Medical Center and Alperin Medical Clinics, Santa Clara, CA. Review provided by VeriMed Healthcare Network.