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Metyrapone test

Definition

The metyrapone test measures the ability of the pituitary gland to release adrenocorticotropic hormone (ACTH) in response to decreased blood cortisol levels.

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, 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.

How to Prepare for the Test

The health care provider may tell you to temporarily stop taking any drugs that may affect test results. This may include rifampin, phenobarbital, or phenytoin. The drugs may have to be stopped for several weeks before to the test.

Other drugs that can affect metyrapone test results include chlorpromazine, corticosteroids, birth control pills, and other estrogen-containing medications.

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 done to determine whether the pituitary gland is working properly.

Normal Results

Normal values for the blood tests:

• 11-deoxycortisol increased to more than 3 micrograms per deciliter (mcg/dL)
• Cortisol less than 7 mcg/dL
• ACTH greater than 75 picograms per milliliter (pg/mL)

A normal value for the 24-hour urine test shows that the baseline excretion of urinary 17-OHCS more than doubled.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

Abnormal results may be due to Cushing syndrome or adrenal insufficiency. The test may help distinguish between the different types of Cushing syndrome.

Risks

• 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

Considerations

Abnormal thyroid function can affect this test.

References

Nieman LK. Dynamic evaluation of adrenal hypofunction. J Endocrinol Invest. 2003;26 & Suppl):74-82.

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