ACTH Stimulation Test

The ACTH stimulation test may be used to investigate a low cortisol test result. It may be used to help diagnose primary adrenal insufficiency (Addison disease) if your healthcare practitioner suspects that your adrenal glands may not be producing enough cortisol. The test may also be done to help determine whether a condition affecting the pituitary gland is causing low cortisol levels (secondary adrenal insufficiency).

This test is used to determine whether your adrenal glands are capable of responding to ACTH and whether this is a typical response.

The Endocrine Society recommends using tests for ACTH, aldosterone (also produced by the adrenal glands) and renin (a hormone that controls aldosterone production) as part of the evaluation for primary adrenal insufficiency.

The ACTH stimulation test may be ordered when you have a low result on a cortisol test and a combination of signs and symptoms that suggest low cortisol or adrenal insufficiency, such as:

• Weight loss
• Muscle weakness
• Fatigue
• Low blood pressure
• Abdominal pain
• Dark patches of skin (this occurs in Addison disease but not secondary adrenal insufficiency)
• Low blood sugar (hypoglycemia, especially in children)

If your adrenal glands are functioning normally, then your cortisol level will rise in response to the ACTH you are given. (The cortisol level in the second sample drawn should be elevated above a certain level and to a certain degree when compared to the baseline sample.) This result rules out primary adrenal insufficiency (Addison disease).

If your adrenal glands are damaged or not functioning properly, then your cortisol level will not increase after you are given ACTH. You may be diagnosed with adrenal insufficiency. Additional testing may be necessary to identify the cause.

The ACTH stimulation test is not a definitive test for adrenal insufficiency due to pituitary damage. If injury to the pituitary occurred only in the previous few weeks, a falsely normal response to ACTH injection may be observed. A repeat ACTH stimulation test 6 to 8 weeks later might then reveal secondary adrenal insufficiency. Other tests may also be considered.

Rarely, there is a problem with the hypothalamus and the production of corticotropin-releasing hormone (CRH). The ACTH stimulation test does not distinguish this problem from other causes of adrenal insufficiency.

Glucocorticoids such as prednisone, hydrocortisone, dexamethasone, etc. are prescribed for a variety of conditions. These medications can suppress cortisol production by the adrenal glands. If you need to stop taking them, your healthcare practitioner will usually taper off your dose so that your adrenal gland cortisol production has time to restart and you avoid “withdrawal” adrenal insufficiency symptoms. In some people who have taken glucocorticoids chronically (especially at high dose) for various medical conditions (other than Addison disease), it may take up to one year for the body to resume normal cortisol production after the glucocorticoids are stopped.

The most common cause of primary adrenal insufficiency in adults in the U.S. is an autoimmune disorder where the body’s immune system attacks the adrenal glands. The most common cause of primary adrenal insufficiency in children in the U.S. is a congenital disease called congenital adrenal hyperplasia (CAH). Other causes in any age group include damage from bleeding into the adrenal glands and infections such as tuberculosis or HIV infection. (For more, see Adrenal Insufficiency and Addison Disease).

Tests for these autoantibodies can help determine the cause of primary adrenal insufficiency. The most common cause of primary adrenal insufficiency in adults (about 75%) is an autoimmune process in which an inappropriate immune response destroys tissues within the adrenal glands. 21-hydroxylase autoantibodies and/or adrenal cytoplasmic autoantibodies are markers of this autoimmune process.

Sometimes, decreased cortisol production combined with a stressor can cause an adrenal crisis that can be life-threatening and requires immediate medical attention. Signs and symptoms of a crisis may include:

• Sudden onset of severe pain in the lower back, abdomen, or legs
• Vomiting and diarrhea, resulting in dehydration
• Low blood pressure (hypotension)
• Loss of consciousness
• Low blood glucose

Adrenal crisis is the most common cause of death in patients with adrenal insufficiency.

Once your healthcare practitioner has identified a problem associated with the adrenal glands, pituitary gland, or other cause, other testing such as CT (computerized tomography) or MRI (magnetic resonance imaging) scans may be performed to locate the source of the problem and to evaluate the extent of any damage to the glands. For more details about these imaging scans, see RadiologyInfo.org.

Since the ACTH stimulation test involves giving an injection of manufactured ACTH, the test can interfere with subsequent tests that measure ACTH levels. Therefore, ACTH testing is not recommended for several hours following an ACTH stimulation test.