ACTH (cosyntropin) stimulation test measures how well the adrenal glands respond to the hormone ACTH. ACTH is a hormone produced in the pituitary gland that stimulates the adrenal glands to release cortisol.

The health care provider will measure the cortisol in your blood before and after an ACTH injection.

Blood is typically drawn from a vein, usually on the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

Once the blood has been collected, the health care provider will use a needle to inject cosyntropin. Other timed specimens are also collected.

Along with the blood tests, sometimes you may also have a urinary free cortisol test or urinary 17-ketosteroids test in which the urine is collected over a 24-hour period.

You may need to limit activities and eat a high-carbohydrate diet 12-24 hours before the test. You may be asked to fast for 6 hours before the test.

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.

This test can help determine whether your adrenal and pituitary glands are normal. It is most often used when the health care provider suspects adrenal gland disorders, such as Addison's disease or pituitary insufficiency.

An increase in cortisol after stimulation by ACTH is normal. Blood cortisol after ACTH stimulation should be greater than 18 - 20 mcg/dL, depending on the dose of cosyntropin used.

Note: mcg/dL = micrograms per deciliter

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

This test is helpful in determining if you have:

• Acute adrenal crisis
• Addison's disease (decreased adrenal output)
• Low pituitary function
• Pituitary tumors

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Stewart PM. The adrenal cortex. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2008: chap 14.

Melmed S, Kleinberg D. Anterior pituitary. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2008: chap 8.