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.
Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will mean. To help you learn about this test and how important it is, fill out the medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
- Bruising may be more likely in people with high ACTH and cortisol levels.
An adrenocorticotropic hormone test measures the level of adrenocorticotropic hormone (ACTH) in the blood.
Results of an ACTH test are usually available in a few days.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Less than 50 pg/mL or less than 11 pmol/L
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.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking medicine, such as corticosteroids, estrogen, or spironolactone. Also, medicines that act like cortisol or cause the release of cortisol, including amphetamines, lithium, and insulin, can affect test results.
- Being drunk (intoxicated).
- Being pregnant or having your period.
- Having a severe injury.
- Physical or emotional stress.
- Having a medical test that uses a radioactive tracer within 1 week before an ACTH test.
There are other medicines that may affect the test results, so talk with your doctor about any medicines you are taking.
What To Think About
- The interpretation of the ACTH test is complicated, because many things can change the results. Blood must be collected in special tubes, placed on ice, and processed quickly. The time of day when the blood is drawn can also change the results. ACTH test results should be compared to medical information gathered from other tests, especially the blood cortisol level. To learn more, see the topic Cortisol in Blood.
- Inferior petrosal sinus sampling is a test that measures the amount of ACTH from a channel (inferior petrosal sinus) near the pituitary gland. This test may be done along with an ACTH blood test when the levels of both ACTH and cortisol are high. It is used to tell the difference between ACTH made by the pituitary gland and ACTH made somewhere else in the body. This test may only be available at large medical centers.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerAlan C. Dalkin, MD - Endocrinology
Current as ofNovember 20, 2015