What is the ACTH (cosyntropin) stimulation test?
Your pituitary gland is a pea-sized gland located at the base of your brain. It produces many types of hormones, including the adrenocorticotropic hormone (ACTH).
ACTH stimulates the adrenal glands, which sit atop the kidneys, to release two hormones: cortisol and adrenaline (also known as epinephrine). These hormones help you respond to stress in a healthy way and support your immune system. Cortisol is a steroid hormone that affects many different systems in the body, including your:
- circulatory system
- immune system
- nervous system
- bone metabolism
- metabolism of nutrients such as carbohydrates, fats, and protein
Adrenaline, or epinephrine, is a hormone responsible for maintaining normal nervous system and circulatory function. This hormone, along with another hormone called norepinephrine, are responsible for your protective fight-or-flight response when you face a stressful situation.
Your healthcare provider might have you take an ACTH (cosyntropin) test if they suspect your adrenal glands aren’t functioning properly. This test requires you to receive an injection of cosyntropin, a synthetic portion of ACTH. You will also have two blood samples drawn — one before the injection and one after the injection. These samples measure the level of cortisol in your blood.
This ACTH stimulation test measures how your adrenal glands react to the ACTH in your blood. It does this by measuring your body’s cortisol levels. It’s important not to confuse this test with an ACTH test, which simply measures the ACTH levels in your blood.
The ACTH stimulation test is used to diagnose adrenal insufficiency, a condition known as Addison’s disease. It is also used to determine if the pituitary gland is not working properly due to hypopituitarism. Deficient cortisol could alternately be a cause of secondary adrenal insufficiency.
The ACTH test, along with the ACTH blood level, is also used to diagnose excessive cortisol secretion from the adrenal gland, as in the case of Cushing’s syndrome.
Below are some of the signs and symptoms that may alert your doctor to order an ACTH stimulation test. These signs are nonspecific. However, they should be evaluated if they’re progressive and interfere with your daily activities and normal functioning:
- unexplained weight loss
- low blood pressure
- loss of appetite
- muscle weakness
- muscle and joint pain
- darkening discoloration of the skin
- mood changes
Some characteristic signs and symptoms of excess secretion of cortisol include:
- round face
- obesity (around trunk)
- increased facial and body hair
- menstrual irregularities in females
- low sex drive in men
Your healthcare provider might order an ACTH (cosyntropin) stimulation test if you experience these symptoms. This can help them decide if malfunctioning adrenal glands are the cause of your symptoms.
Slight risks are present any time you have blood drawn. These include:
- excessive bleeding
- inflammation of the vein at the site of entry of the blood drawing
You will probably feel mild to moderate pain when the needle is inserted. You might also feel throbbing in the puncture site after the needle has been removed. There may be mild bleeding following withdrawal of the needle, and you could develop a small bruise in the area. All of these symptoms are limited and do not cause any serious lasting effects.
Preparation for this test can vary. Make sure to get clear instructions from your healthcare provider. You will likely need to fast for eight hours before the test. Your provider might advise you to stop taking certain medications for 24 hours prior to testing. Some common medications that can affect cortisol levels include (but are not limited to):
- steroid medications
- male hormones
- birth control pills
- phenytoin (antiseizure drug)
It’s important to make sure your doctor knows about all the medications you’re taking, including over-the-counter drugs.
A healthcare provider will take a blood sample when you arrive for your procedure. This blood sample will measure your blood cortisol levels. Your doctor can use this sample as a baseline against which to compare the results of the second blood test.
You will receive an injection of cosyntropin, a synthetic portion of ACTH. This hormone should trigger the adrenal glands to produce cortisol. You will then wait for about an hour while your body reacts to the cosyntropin injection.
Your healthcare provider will take a second blood sample after this first hour is up. This sample will reflect your cortisol levels after your body has had time to react to the injection.
Both of your blood samples will be tested for their cortisol levels. You will typically get the results of your ACTH stimulation test in one to two weeks.
Your blood’s cortisol levels should rise with the ACTH stimulation if your adrenal glands are functioning as they should. Test results may vary slightly, so talk to your doctor if you are concerned.
Blood cortisol levels below the acceptable range following stimulation are considered low. These abnormal results on the ACTH stimulation test may mean that you have an adrenal condition such as acute adrenal crisis, Addison’s disease, or hypopituitarism.
Blood cortisol levels above the expected range following ACTH stimulation may be consistent with Cushing’s syndrome. Further testing is required to confirm this diagnosis. This testing process can be complicated, so be sure to talk to your healthcare provider about how to proceed.