What Is an ACTH Test?
An ACTH test is a type of blood test. It measures how much of a hormone you have called ACTH (adrenocorticotropic hormone). This test should not be confused with an ACTH stimulation test.
Other names for ACTH are:
- Serum adrenocorticotropic hormone
- Highly-sensitive ACTH
Cortisol is a hormone with some important jobs. It helps:
- Control your blood pressure
- Your body respond properly to infections
- Break down sugar, fat, and protein in your food
Your doctor might want you to be tested if they think your pituitary or adrenal glands are making too much or too little ACTH or cortisol.
An ACTH test is usually done alongside a cortisol test. That’s because the symptoms of too much or too little ACTH mostly come from having too much or too little cortisol.
Symptoms of too much cortisol from excess ACTH are:
- Weight gain
- Extra fat in the shoulders
- Pink or purple marks on parts of you body
- Bruising easily
- More body hair
- Muscle weakness
Symptoms of too little cortisol are:
- Weight loss
- Nausea or vomiting
- Belly pain
- Dark spots on the skin
- Craving salt
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
- A tumor outside the pituitary gland
- Poor hormone production by your pituitary and adrenal glands
ACTH Test Preparation
If you take steroids, you’ll need to stop for up to 48 hours before the test. Steroids can affect the test 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 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.
ACTH Test 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.
ACTH Test Risks
The risks are the same as with any test that uses a needle to take blood. They include:
- Looking pale
- Drop in heart rate or blood pressure
ACTH Test Results
Your results can vary from lab to lab. They might also be different depending on what time of day the test was taken.
ACTH is measured in picograms per milliliter (pg/mL) of blood. 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.