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ACTH stimulation test

This test checks how the adrenal glands respond to a certain hormone, called adrenocorticotrophic hormone, abbreviated as ACTH.

ACTH is made in the pituitary gland and travels through the bloodstream to the adrenal glands. ACTH stimulates the adrenal gland to release cortisol. Cortisol is a key factor in many functions in the body's metabolism of fats, carbohydrates, sodium, potassium, and protein.

Who is a candidate for the test?

This test is ordered when the doctor suspects that a person's adrenal gland is not working the way it should.

How is the test performed?

Cortisol levels in the bloodstream are measured before and after an injection of ACTH into the blood or muscle. A blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, called a tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.

What is involved in preparation for the test?

A person should request specific instructions from his or her healthcare professional.

What do the test results mean?

In a healthy person, an injection of ACTH will stimulate the adrenal glands. An increase in cortisol results.

If cortisol levels do not rise after the injection of ACTH, one of the following conditions may be present:

• acute adrenal crisis, which is a condition in which the adrenal glands suddenly stop working the way they should
• Addison disease, which can be caused by inadequate response of a damaged adrenal gland to ACTH
• Cushing syndrome, which can happen when the adrenal gland is already overproducing cortisol regardless of the input of ACTH
• hypopituitarism, which is a decrease in activity of the pituitary gland
• pituitary tumor, which is an abnormal growth in the pituitary gland