Your pituitary is a pea-sized gland at the base of the brain that produces ACTH (adrenocorticotropic hormone). This hormone, in turn, causes the adrenal glands (which sit at the top of your kidneys) to make cortisol.
Cortisol is a hormone with some important jobs:
- It helps regulate your blood pressure.
- It helps your body respond properly to infections.
- It helps break down sugar, fat, and protein in your food.
Your doctor might want you to be tested if he suspects your pituitary or adrenal glands are producing too much or too little ACTH or cortisol.
What Does the Test Measure?
An ACTH test is usually done alongside a cortisol test.
By measuring the ACTH in your blood, your doctor can also learn whether you have a number of other conditions, including:
- Cushing’s syndrome
- Cushing’s disease
- Addison’s disease
- Poor hormone production by your pituitary and adrenal glands
How Should I Prepare for the Test?
If you take steroids, you’ll need to stop for up to 48 hours before the test. Steroids may cause abnormal results.
Your doctor might ask you to limit your carbohydrates in the 48 hours leading up to the test, as well.
- Avoid eating or drinking after midnight.
- Get a good night’s sleep.
- Avoid exercise in the 12 hours before the test.
- Avoid emotional stress and exercise in the 12 hours before the test.
- Make sure your doctor knows about any prescription or nonprescription medicine, supplements, vitamins, herbs and recreational or illicit drugs you’re taking.
What Happens During the Procedure?
Your doctor will take some samples of your blood.
Because your hormone levels change during the day, you may have to have this done in the morning and once more later in the day. That will give your doctor the peak level and the low level. In most cases ACTH is highest early in the morning and lowest in the evening.
After your blood sample has been taken, the samples are placed on ice and processed quickly.
What Are the Risks?
There are few serious ones. Taking a blood sample using a needle carries the risk of an infection, bleeding and bruising. The spot where the needle stuck your arm may also be sore.
What Do the Results Mean?
You’ll typically receive them in a few days.
ACTH is measured in picograms per milliliter (pg/ml) of blood. A picogram is one-trillionth of a gram. A milliliter is one-thousandth of a liter.
Results also vary somewhat from lab to lab. They might also be different depending on what time of day the test was taken. Adults normally have ACTH levels of 10-50 pg/ml at 8 a.m. The number drops to below 5-10 pg/ml at midnight.
Other things that could affect your test results include:
- How well you slept the night before the test
- Whether you’re under a lot of stress
- Being pregnant or on your period
- Whether you’re taking certain drugs like hormones, insulin or steroids
- Having experienced a recent trauma
- Depression, especially in the elderly
- Whether the blood samples were collected and stored properly (on ice, not room temperature)
Because they’re related, ACTH and cortisol levels are typically looked at together.
If your ACTH results aren’t as they should be, your doctor will likely want more tests done to confirm the results and look for a cause.