What does a high ACTH level indicate?

Elevated ACTH usually points to the pituitary or hypothalamus over‑producing the hormone, as seen in Cushing’s disease (pituitary adenoma) or ectopic ACTH‑secreting tumors. It can also occur when the adrenal glands are not making enough cortisol (primary adrenal insufficiency), prompting the pituitary to release more ACTH to compensate.

Can any medications interfere with ACTH test results?

Yes. Systemic glucocorticoids, oral contraceptives, phenytoin, carbamazepine, and some antifungal agents can either suppress or falsely elevate ACTH or cortisol. Always give your lab a complete medication list; your provider may ask you to stop certain drugs several days before testing, if medically safe.

How should I prepare for an ACTH stimulation test?

Your doctor will likely ask you to fast for 8‑12 hours before the test and avoid stress‑inducing activities. Bring a list of all prescription, over‑the‑counter, and herbal medicines because many drugs (e.g., glucocorticoids, estrogen, certain antihistamines) can alter ACTH or cortisol levels. If you take steroid inhalers or topical steroids, discuss whether you need to pause them temporarily.

What does a low ACTH level mean?

Low ACTH often suggests that cortisol is already high, suppressing pituitary output—common in adrenal tumors that produce excess cortisol (secondary Cushing’s). It can also be seen after prolonged exogenous steroid use, which shuts down the body’s own ACTH production.

Adrenocorticotropic Hormone (ACTH)

An ACTH test measures the level of this hormone in your blood to help diagnose and monitor conditions affecting your adrenal and pituitary glands.

What is an adrenocorticotropic hormone (ACTH) test?

This test measures the level of adrenocorticotropic hormone (ACTH) in a sample of your blood. A hormone is a chemical messenger in your bloodstream that controls the actions of certain cells or organs. ACTH tells your adrenal glands, two small glands that sit above your kidneys, to make another hormone called cortisol.

Cortisol affects almost every organ and tissue in your body. It helps your body:

Respond to stress (cortisol is sometimes called the "stress hormone")
Reduce inflammation
Regulate blood glucose, also called blood sugar, and metabolism (how your body uses food for energy)
Control blood pressure

Because ACTH controls how much cortisol you make, ACTH testing is usually done with a blood test to measure your cortisol levels. Normally, if cortisol levels drop too low, your ACTH levels will increase to trigger your adrenal glands to make more cortisol. If cortisol levels are high, ACTH levels will decrease so your adrenal glands will make less cortisol.

Your ACTH and cortisol levels are controlled by a complex feedback system involving:

Pituitary gland: A small gland at the base of your brain that makes ACTH and other hormones.
Hypothalamus: A part of your brain that makes a hormone telling your pituitary gland how much ACTH to make.
Adrenal glands: These glands respond to ACTH by making cortisol and releasing it into your bloodstream.

What is it used for?

An ACTH test is used to help diagnose and monitor conditions that affect cortisol levels, including disorders of the pituitary and adrenal glands.

High cortisol levels

High levels may be caused by:

Cushing's disease: A usually benign tumor in the pituitary gland that produces too much ACTH, triggering the adrenal glands to overproduce cortisol.
Cushing's syndrome: A disorder caused by long-term exposure to too much cortisol, which may result from long-term use of high-dose steroid medicine, adrenal gland tumors, or rare tumors outside the pituitary gland that produce ACTH.

Low cortisol levels

Low levels may be caused by:

Addison disease: A condition where the adrenal glands are damaged—usually by autoimmune disease—and cannot make enough cortisol.
Hypopituitarism: A rare disorder where the pituitary gland fails to produce enough hormones, including ACTH, often due to tumors, damage to the gland, or problems with the hypothalamus.

Why do I need an ACTH test?

You may need this test if you have had abnormal results on a cortisol test or exhibit symptoms of cortisol imbalance.

Symptoms of too much cortisol

Weight gain
Thin arms and legs
Round face
Increased fat around the base of the neck or between the shoulder blades
Easy bruising
Wide purple streaks on the stomach, breasts, hips, and under the arms
Muscle weakness

Symptoms of too little cortisol

Long-lasting fatigue
Muscle weakness
Loss of appetite
Weight loss
Abdominal (belly) pain

What happens during an ACTH test?

A health care professional will take a blood sample from a vein in your arm using a small needle. The process typically takes less than five minutes.

Preparation and Risks

Your provider may require you to fast for several hours before the test. Blood samples are often collected early in the morning when ACTH levels are naturally at their highest. Inform your provider of all medications you are taking, but do not stop taking them unless instructed. Risks are minimal, typically limited to slight pain or bruising at the needle site.

What do the results mean?

Providers compare ACTH levels with cortisol levels to interpret results:

High ACTH and high cortisol: Often a sign of Cushing's disease (pituitary tumor).
High ACTH and low cortisol: A sign of Addison disease (adrenal gland damage).
Low ACTH and high cortisol: A sign of Cushing's syndrome, potentially from steroid use or an adrenal tumor.
Low or normal ACTH and low cortisol: A sign of hypopituitarism.