Adrenocorticotropic hormone (ACTH) is a hormone that the pituitary gland produces. Its main function is to stimulate the adrenal glands to produce and secrete another hormone called cortisol.
Some people refer to cortisol as the body’s stress hormone. Cortisol helps control a wide range of processes throughout the body, including metabolism and immune responses.
A doctor can perform an ACTH test to measure how much ACTH a person is producing. This can help diagnose conditions that impact the adrenal and pituitary glands, which can result in unusual levels of cortisol.
This article discusses the function of ACTH, the purpose of an ACTH test, and how to interpret test results.
ACTH is a
The body uses the hypothalamic-pituitary-adrenal (HPA) axis to control the level of ACTH and cortisol. HPA axis refers to the communication between these regions of the body to regulate hormone levels.
When cortisol levels are low, the hypothalamus releases a hormone called corticotrophin-releasing hormone (CRH). This hormone acts on the pituitary gland and stimulates it to release ACTH into the bloodstream. The adrenal gland detects high levels of ACTH, which stimulates it to release cortisol.
As cortisol levels begin to rise, the hypothalamus starts to slow the release of CRH, which in turn slows the release of ACTH from the adrenal glands. ACTH levels start to drop as a result, which also causes cortisol levels to decline. Health experts refer to this as a negative feedback loop. This communication helps to regulate hormone levels and stop the body from producing too much or too little.
The main purpose of an ACTH test is to evaluate the function of ACTH by measuring ACTH levels. This can help doctors diagnose conditions that impact pituitary or adrenal gland function. These conditions can include:
- Cushing’s disease, where the pituitary gland makes too much ACTH
- Cushing’s syndrome, where the adrenal glands produce too much cortisol
- Addison’s disease, where the adrenal glands do not make enough cortisol
- hypopituitarism, a condition where the pituitary does not produce enough hormones
- adrenal or pituitary tumors, which can impact hormone production
A doctor will typically recommend this test if a person displays symptoms of too much or too little cortisol. They will also usually advise a cortisol level test. Symptoms of too much cortisol can include:
- weight gain
- fat accumulation on the back of the neck and shoulders
- easily bruising
- muscle weakness
- increased body hair
- pink or purple stretch marks
Symptoms of too little cortisol may include:
A doctor can also use an ACTH test to help monitor conditions that involve excessive or deficient levels of hormones.
To perform an ACTH test, medical staff will require a blood sample. This will involve drawing blood through a needle from a vein in the arm. Medical staff will typically disinfect an area on the arm, then place an elastic band further up the arm. This will help to make the veins more prominent. They will then enter a vein with a needle, then use a syringe to draw blood.
Both ACTH and cortisol follow a circadian rhythm, meaning levels are usually higher in the morning and lowest during sleep. Additionally, as the blood sample typically requires immediate processing, health experts often perform ACTH tests in the morning, at about 9 a.m. However, a person may have their blood drawn at different points during the day to check for variations in ACTH levels.
The sample will then go to a laboratory, which is often on-site in the hospital where staff are collecting the sample. After testing the blood for hormone levels, laboratory staff will send the results to a person’s doctor. The doctor will then interpret the results and discuss them with the individual.
A person will typically undergo an ACTH test if they have symptoms that suggest an adrenal or pituitary condition, or they have unusual cortisol levels.
For an early morning sample, health experts consider 10–60 picograms per milliliter (pg/mL), or 1.3–16.7 picomoles per liter (pmol/L), as a normal range. These values may vary slightly depending on the laboratory.
In some cases, the results of the test may not be clear. In these situations, health experts may use synthetic versions of ACTH and cortisol to help with the diagnosis. For example, they may use tetracosactide, a drug version of ACTH, to determine if it tells the adrenal glands to produce cortisol. Similarly, they may use dexamethasone, a drug that acts like cortisol, to see if it stops ACTH production.
Some factors may impact results, such as if a person:
As the ACTH test requires a blood sample, potential risks are similar to other tests that involve taking blood. This can include:
- feeling dizzy
- pain at the injection site
Adrenocorticotropic hormone is an important hormone that the pituitary gland secretes. Its main function is regulating another hormone known as cortisol, which has a role in many bodily functions. The level of ACTH in the blood dictates how much cortisol the adrenal glands release.
Doctors can measure the levels of these hormones to help determine if the pituitary and adrenal glands are functioning properly and help diagnose health conditions. For example, high ACTH levels may indicate Cushing’s disease or Addison’s disease, while low ACTH can suggest an adrenal tumor or hypopituitarism.