Adrenocorticotropic Hormone (ACTH) Test
ACTH is made in the pituitary gland in response to the release of another hormone, called corticotropin-releasing hormone (CRH), by the hypothalamus. In turn, the adrenal glands then make a hormone called cortisol, which helps your body manage stress. Cortisol is needed for life, so its levels in the blood are closely controlled. When cortisol levels rise, ACTH levels normally fall. When cortisol levels fall, ACTH levels normally rise.
Both ACTH and cortisol levels change throughout the day. ACTH is normally highest in the early morning (between 6 a.m. and 8 a.m.) and lowest in the evening (between 6 p.m. and 11 p.m.). ACTH levels may be tested in the morning or evening if your doctor thinks that they are abnormal. Cortisol levels are often measured at the same time as ACTH.
ACTH is released in bursts, so its levels in the blood can vary from minute to minute. Interpretation of the test results is hard and often requires the skill of an endocrinologist.
Why It Is Done
A test to measure ACTH is done to check for:
- A problem with the adrenal glands or pituitary gland. A high level of ACTH and a low level of cortisol (or low ACTH and high cortisol levels) could be caused by a problem with the adrenal glands. Low levels of ACTH and cortisol could be caused by a problem with the pituitary gland.
- Overproduction of ACTH. This may be caused by an overactive pituitary gland, or sometimes by a tumor in the lung. In response, the adrenal glands release too much cortisol (one form of Cushing's syndrome).
How To Prepare
You may not be able to eat or drink for 10 to 12 hours before an ACTH test. Your doctor may ask you to eat low-carbohydrate foods for 48 hours before the test. Be sure to ask your doctor if there are any foods that you should not eat.
Many medicines can change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take. If you take a medicine, such as a corticosteroid, that could change the test results, you will need to stop taking it for up to 48 hours before the test. Your doctor will tell you exactly how long depending on what medicine you take.
Do not exercise for 12 hours before this test.
Try to avoid emotional stress for 12 hours before the test.
Collecting the blood sample at the right time is often important. Your blood will be drawn in the morning if your doctor wants a peak ACTH level. Your blood will be drawn in the evening if your doctor wants a low (trough) ACTH level.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site. Bruising may be more likely in people with high ACTH and cortisol levels.
Results of an ACTH test are usually available in a few days.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
High levels of ACTH may be caused by:
- Emotional or physical stress (such as recent surgery or severe pain).
- Diseases such as Addison's disease (failure of the adrenal glands), Cushing's disease (a tumor of the pituitary gland), or a tumor outside the pituitary (such as in the lung).
Low levels of ACTH may be caused by:
- Damage to the pituitary gland from surgery, radiation, stroke, head injury, or a tumor.
- An increased amount of cortisol from a tumor in the adrenal glands (Cushing's syndrome).
- Corticosteroid medicines.