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| Definition: |
A test that measures the ability of the pituitary gland to secrete ACTH in response to decreased serum cortisol.
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| How the test is performed: |
| There are two different types of metyrapone tests. The first is an overnight test where 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.
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| 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 physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| 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 synthesis 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 synthesize cortisol. Since the enzyme is inhibited, 11-deoxycortisol accumulates and eventually appears in the blood and urine. |
| Normal Values: |
blood:
- 11-deoxycortisol increased to more than 7 mcg/dl
- cortisol less than 10 mcg/dl
24-hour urine:
- baseline excretion of urinary 17-OHCS more than doubled
Note: mcg/dl = micrograms per deciliter |
| What abnormal results mean: |
| The test may be useful in differentiating 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
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| Special considerations: |
| Not applicable. |
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Review Date: 3/13/2002
Reviewed By: Todd T. Brown, M.D., Division of Endocrinology and Metabolism, Johns Hopkins Hospital, Baltimore, MD. Review provided by VeriMed Healthcare Network.
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