Adrenocorticotropic Hormone (ACTH) Test
Reviewed
Also called: Adrenocorticotropic hormone blood test, corticotropin
This test measures the level of adrenocorticotropic hormone (ACTH) in your blood. ACTH is a hormone that tells your adrenal glands to produce cortisol, which affects many body functions. The test is used to help diagnose and monitor conditions that cause too much or too little cortisol, such as Cushing's disease, Addison disease, or hypopituitarism. Your provider will compare your ACTH and cortisol levels to interpret the results.
Specimen: Blood
Why this test may be ordered
- To help diagnose the cause of abnormal cortisol levels
- To evaluate symptoms of too much cortisol (e.g., weight gain, easy bruising) or too little cortisol (e.g., fatigue, weight loss)
- To monitor conditions affecting the pituitary or adrenal glands
Preparation and collection
Your provider will give you specific instructions. You may need to fast (not eat or drink) for several hours before the test. Blood samples are often taken early in the morning when ACTH levels are highest. You may need to stop taking certain medicines before the test, but do not stop any medication unless your provider tells you to.
Blood sample from a vein in the arm
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.
Understanding results
To understand what your ACTH test results mean, your provider will usually compare your ACTH level with your cortisol level. Abnormal results alone do not diagnose a condition; they help identify possible causes that require further testing. Always discuss your results with your healthcare provider.
- High ACTH and high cortisol levels: May indicate a pituitary tumor that produces too much ACTH (Cushing's disease), or rarely a tumor elsewhere that also makes ACTH. Limitation: This pattern suggests a possible condition but is not diagnostic by itself. Next step: You may need a CT or MRI scan to confirm whether you have a pituitary tumor, or other tests to check for tumors in the lung, pancreas, or thyroid gland.
- High ACTH and low cortisol levels: May indicate damage to the adrenal glands (Addison disease), where the pituitary gland tries to increase ACTH to compensate. Limitation: This pattern suggests a possible condition but is not diagnostic by itself. Next step: Your provider may recommend additional tests to evaluate the function of your adrenal glands.
- Low ACTH and high cortisol levels: May indicate Cushing's syndrome, often due to long-term steroid use or an adrenal gland tumor that produces extra cortisol. Limitation: This pattern suggests a possible condition but is not diagnostic by itself. Next step: Your provider may check for long-term use of steroid medicines or perform imaging to look for adrenal gland tumors.
- Low or normal ACTH and low cortisol levels: May indicate hypopituitarism, where the pituitary gland does not produce enough ACTH, leading to low cortisol. Limitation: This pattern suggests a possible condition but is not diagnostic by itself. Next step: Your provider may recommend tests to assess pituitary function and imaging to look for pituitary tumors or damage.
- Results are not sufficient for diagnosis on their own.
- Your healthcare provider will interpret your ACTH and cortisol levels together.
- Additional tests are often needed to confirm the specific cause of abnormal results.
What to do next
Your provider may recommend additional tests such as a CT or MRI scan, or an ACTH stimulation test to further evaluate the cause of abnormal results.
- What do my ACTH and cortisol levels together indicate?
- Will I need additional tests to confirm the diagnosis?
- How should I prepare for the test, especially regarding fasting and medications?
Evidence source
U.S. National Library of Medicine: Adrenocorticotropic Hormone (ACTH) Test