Adrenocorticotropic Hormone (ACTH)

What is an adrenocorticotropic hormone (ACTH) test?

This test measures the level of adrenocorticotropic hormone (ACTH) in a sample of your blood. A hormone is a chemical messenger in your bloodstream that controls the actions of certain cells or organs. ACTH tells your adrenal glands, two small glands that sit above your kidneys, to make another hormone called cortisol.

Cortisol affects almost every organ and tissue in your body. It helps your body:

• Respond to stress (cortisol is sometimes called the "stress hormone")
• Reduce inflammation
• Regulate blood glucose, also called blood sugar, and metabolism (how your body uses food for energy)
• Control blood pressure

Because ACTH controls how much cortisol you make, ACTH testing is usually done with a blood test to measure your cortisol levels. Normally, if cortisol levels drop too low, your ACTH levels will increase to trigger your adrenal glands to make more cortisol. And if cortisol levels are high, ACTH levels will decrease so your adrenal glands will make less cortisol.

Your ACTH and cortisol levels are controlled by a complex feedback system of hormones made in different parts of your body. These include your:

• Pituitary gland. This small gland is in the base of your brain. It makes ACTH and other hormones.
• Hypothalamus. This is a part of your brain. It makes a hormone that tells your pituitary gland how much ACTH to make.
• Adrenal glands. These glands respond to ACTH by making cortisol and releasing it into your bloodstream. The increased amount of cortisol in your blood signals your hypothalamus to stop making the hormone that tells your pituitary to make ACTH.

Conditions that affect any part of this system can affect the amount of cortisol in your body. Too much or too little cortisol can lead to serious health problems.

Other names: Adrenocorticotropic hormone blood test, corticotropin

What is it used for?

An ACTH test is used to help diagnose and monitor conditions that affect cortisol levels. These conditions include disorders of the pituitary and adrenal glands.

High cortisol levels may be from:

• Cushing's disease, a tumor in the pituitary gland that's usually benign (not cancer). The tumor makes too much ACTH, which triggers the adrenal glands to make too much cortisol. The tumor keeps making ACTH even when cortisol levels are high.
• Cushing's syndrome, a disorder in which your body is exposed to too much cortisol over a long period of time. The extra cortisol may be caused by:
  • Long-term use of high doses of steroid medicine. Steroids can have side effects that increase cortisol levels.
  • Tumors in the adrenal glands that make extra cortisol, even when blood cortisol levels are high.
  • Tumors outside of the pituitary gland that make extra ACTH. This triggers the adrenal glands to make too much cortisol. These tumors are often found in the lungs, but they aren't common.

Low cortisol levels may be from:

• Addison disease, a condition in which the adrenal glands can't make enough cortisol because they are damaged. The damage is usually caused by autoimmune disease.
• Hypopituitarism, a condition in which the pituitary gland either stops making one or more hormones or can't make enough hormones, including ACTH. This rare disorder may be caused by pituitary tumors, damage to the pituitary gland, or a problem with the hypothalamus. If the pituitary gland can't make enough ACTH, the adrenal glands won't make enough cortisol.

ACTH and cortisol tests are used together to help find out which type of condition may be causing abnormal cortisol levels. Other tests are often needed to help make a final diagnosis.

Why do I need an ACTH test?

You may need this test if you had abnormal results on a cortisol test or have symptoms of too much or too little cortisol.

Symptoms of too much cortisol may vary. They may include:

• Weight gain
• Thin arms and legs
• Round face
• Increased fat around the base of the neck or between the shoulder blades
• Easy bruising
• Wide purple streaks on the stomach, breasts, hips, and under the arms
• Muscle weakness

Symptoms of too little cortisol include:

• Long-lasting fatigue
• Muscle weakness
• Loss of appetite
• Weight loss
• Abdominal (belly) pain

You may also need this test if you have symptoms of hypopituitarism. Symptoms will vary depending on which pituitary hormones are affected and how low the levels are. If ACTH is decreased, you may have symptoms from low cortisol levels. If a tumor is causing hypopituitarism, symptoms may also include headaches and vision problems.

What happens during an ACTH test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Your health care provider will tell you how to prepare for your test. You may need to fast (not eat or drink) for several hours before your test. Blood samples for ACTH testing are often taken early in the morning when ACTH levels are at their highest for the day.

You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

To understand what the results of your ACTH test mean, your provider will usually compare your ACTH level with your cortisol level. If your results are abnormal, you may need other tests to confirm the specific cause. Ask your provider to explain what your test results say about your health.

In general:

• High ACTH and high cortisol levels are a sign of pituitary tumor that makes ACTH (Cushing's disease). The extra ACTH triggers your adrenal glands to make too much cortisol.

  You'll likely need more tests, such as a CT or MRI scan, to confirm whether you have a pituitary tumor. The high level of ACTH could also be from other causes including:
  • A rare type of tumor in your lung, pancreas, or thyroid gland
  • A condition called multiple endocrine neoplasia
• High ACTH and low cortisol levels are a sign of damage to your adrenal glands (Addison disease). If your adrenal glands can't make enough cortisol, your pituitary gland usually makes more ACTH to try to get your adrenal glands to work better.
• Low ACTH and high cortisol levels are a sign of Cushing's syndrome. This means that high cortisol levels may be caused by long-term use of steroid medicines or an adrenal gland tumor that makes extra cortisol. The high cortisol levels signal your hypothalamus and pituitary gland to decrease ACTH levels.
• Low or normal ACTH and low cortisol levels are a sign of hypopituitarism. This means that a pituitary tumor or damage to your pituitary gland may prevent it from making enough ACTH. Without enough ACTH, your adrenal glands aren't stimulated to make enough cortisol. Over time, they may shrink.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an ACTH test?

Several other tests may be used to help diagnose the specific cause of abnormal cortisol levels. These tests measure changes in your ACTH or cortisol levels after you are given medicines that either trigger or stop the production of the hormones involved with making cortisol.

For example, an ACTH stimulation test is commonly used to help find out if a problem with your adrenal glands is causing low cortisol levels. This blood test measures your cortisol levels before and after you get an injection (shot) of ACTH. The results show whether your adrenal glands are able to respond normally to ACTH by making cortisol.

If your adrenal glands make a normal amount of cortisol after the shot, it suggests that a problem with your hypothalamus or pituitary gland is causing low cortisol levels. If your adrenal glands make little or no cortisol after the shot, you most likely have a problem that affects the health of your adrenal glands.