Metyrapone test measures the ability of the pituitary gland to secrete ACTH in response to decreased serum cortisol.
How the test is performed
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 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 and 11-deoxycortisol may also be drawn.
How to prepare for the test
The health care provider may advise you to temporarily discontinue drugs that may affect the test. 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.
Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
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.
Why the test is performed
The test is used to determine whether the pituitary gland is functioning properly. Metyrapone inhibits an enzyme (steroid 11-beta hydroxylase) involved in the construction of the steroid hormone cortisol (that is, it 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.
- 11-deoxycortisol increased to more than 7 mcg/dl
- Cortisol less than 10 mcg/dl
- Baseline excretion of urinary 17-OHCS more than doubled
Normal value ranges may vary slightly among different laboratories.
Note: mcg/dl = micrograms per deciliter
What abnormal results mean
The test may be useful in distinguishing between the different types of Cushing’s syndrome. In addition, it can sometimes help diagnose adrenal insufficiency.
What the risks are
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
by David A. Scott, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.