ACTH Stimulation Test

An ACTH (cosyntropin) stimulation test assesses how well your adrenal glands respond to adrenocorticotropic hormone. Healthcare providers use this test to help diagnose primary and secondary adrenal insufficiency.


What is an ACTH stimulation test?

An ACTH stimulation test, also known as a cosyntropin stimulation test (CST), is a dynamic medical test that assesses how well your adrenal glands respond to adrenocorticotropic hormone (ACTH). This test is the main medical test to diagnose adrenal insufficiency — either primary, secondary or tertiary adrenal insufficiency.

An ACTH stimulation test involves a shot into your muscle of synthetic ACTH (cosyntropin) and multiple blood draws at different intervals to check your cortisol levels to assess how your adrenal glands respond.

ACTH, or adrenocorticotropic hormone, is a hormone your pituitary gland releases that plays a large role in how your body responds to stress. The release of ACTH triggers your adrenal glands to produce cortisol, the “stress hormone.” Cortisol is an essential hormone that affects almost every organ and tissue in your body.

Primary adrenal insufficiency happens when your adrenal glands don’t produce enough cortisol due to some type of damage to them. Addison’s disease, an autoimmune disease, is the most common cause of primary adrenal insufficiency.

Secondary adrenal insufficiency happens when your pituitary gland doesn’t release enough ACTH to appropriately stimulate your adrenal glands to release cortisol. This could be due to an issue with your pituitary gland.

Tertiary adrenal insufficiency happens when your hypothalamus (an area of your brain) doesn’t make enough corticotropin-releasing hormone (CRH), a hormone that tells your pituitary gland to make ACTH.


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When would I need an ACTH stimulation test?

An ACTH test can help determine whether your adrenal glands and pituitary gland are working properly in terms of cortisol production.

Your healthcare provider may order an ACTH stimulating test for the following reasons:

  • If you had a low cortisol test result.
  • If you have symptoms of adrenal insufficiency.
  • To see if your pituitary and adrenal glands have recovered from prolonged use of glucocorticoid medicines, such as prednisone.

Who performs an ACTH stimulation test?

A nurse will inject the shot of synthetic ACTH. A healthcare provider called a phlebotomist usually performs blood draws, including those needed for an ACTH stimulation test. They then send the collected samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.

You may need to have an ACTH test in a hospital setting or in an endocrinologist’s office, since it involves an injection of synthetic ACTH as well as blood samples. An endocrinologist is a healthcare provider that specializes in hormone-related conditions.


Test Details

Do I need to do anything to prepare for an ACTH stimulation test?

You may need to limit activities and eat foods that are high in carbohydrates 12 to 24 hours before your ACTH stimulation test. You may also need to fast for six hours before the test, which means not eating or drinking anything except water. Your healthcare provider may have you temporarily stop taking certain medications that can interfere with the cortisol blood test.

Since cortisol levels normally vary throughout the day, peaking in the morning, you may need to have your ACTH stimulation test in the morning to minimize the risk of a false-positive result.

In any case, your provider will give you specific instructions for your ACTH stimulation test. Be sure to follow them.

How does an ACTH stimulation test work?

The basic steps of an ACTH stimulation test include:

  1. A phlebotomist will take a blood sample from a vein in your arm for an initial, baseline level of your cortisol levels and potentially other substances in your blood.
  2. A nurse will give you an injection of synthetic ACTH (cosyntropin) through a shot into your muscle. The synthetic ACTH acts like your body’s natural ACTH and stimulates your adrenal glands to produce cortisol.
  3. A phlebotomist will take a blood sample from your vein again to measure your cortisol levels after a specified amount of time — usually 30 minutes and 60 minutes.
  4. A phlebotomist will send your blood samples to a laboratory for testing.


What should I expect during an ACTH stimulation test?

You can expect to experience the following during a blood test, or blood draw:

  • You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
  • Once they’ve located a vein, they’ll clean and disinfect the area.
  • They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
  • After they insert the needle, a small amount of blood will collect in a test tube.
  • Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
  • They’ll place a bandage over the site.

When a nurse gives you a shot injection of cosyntropin, it’ll likely be in your upper arm near your shoulder. The injection may cause moderate pain or stinging, but this will be temporary.

What should I expect after my ACTH stimulation test?

After a healthcare provider has collected your blood samples, they’ll send them to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.

What are the risks of an ACTH stimulation test?

Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

When should I know the results of my ACTH stimulation test?

It may take one week to get your ACTH stimulation test results back. This is because it requires careful interpretation by your provider once the laboratory processes the samples.

Results and Follow-Up

What type of results do you get for an ACTH stimulation test?

Blood test reports, including cortisol blood test reports from an ACTH stimulation test, usually provide the following information:

  • The name of the blood test or what was measured in your blood.
  • The number or measurement of your blood test result.
  • The normal measurement range for that test.
  • Information that indicates if your result is normal or abnormal or high or low.

What are normal results for an ACTH stimulation test?

Under normal circumstances, your cortisol levels should increase after synthetic ACTH stimulation. In a normal result, your cortisol level after ACTH stimulation should be higher than 12.6 micrograms per deciliter (mcg/dL).

Normal reference ranges vary from laboratory to laboratory, test to test and person to person. Always reference the normal reference range given on your report when looking at your results.

In the case of an ACTH stimulation test, your healthcare provider or endocrinologist may need to interpret your results before you see the results yourself. If you have any questions about your results, be sure to ask your provider.

What do abnormal results of an ACTH stimulation test indicate?

Your healthcare provider or endocrinologist will carefully interpret your ACTH test results. Many factors can affect the accuracy of the tests. One of the most common causes of a false-positive test is the recent use of corticosteroids (steroids).

Abnormal ACTH stimulation test results typically indicate primary and secondary adrenal insufficiency.

Primary adrenal insufficiency

If you have primary adrenal insufficiency, your adrenal glands can’t make cortisol or don’t respond appropriately to ACTH. Because of this, you’ll have little or no increase in cortisol levels after an ACTH stimulation test because the synthetic ACTH doesn’t have an effect on your adrenal glands.

Secondary adrenal insufficiency

Prolonged hypopituitarism (underactive pituitary gland) that affects ACTH release and thus results in secondary adrenal insufficiency usually causes your adrenal glands to atrophy (waste away, or degenerate) because the cells that normally make ACTH aren’t being stimulated.

Because of this, if you’ve had hypopituitarism and secondary adrenal insufficiency for a while, you’ll likely have little or no increase in cortisol levels after an ACTH stimulation test.

If the hypopituitarism is partial — meaning your pituitary gland still releases some ACTH — or very recent, you may still have an increase in cortisol levels, or “normal” levels, after an ACTH stimulation test.

A note from Cleveland Clinic

An ACTH stimulation test is the go-to test to diagnose adrenal insufficiency. While it can be stressful to wait for the results of a diagnostic test, know that your healthcare team is there to support you no matter what the results are. Don’t be afraid to ask your healthcare provider questions about your test or results.

Medically Reviewed

Last reviewed on 09/12/2022.

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