Also Known As
Adrenocorticotropic Hormone (ACTH) stimulation test
Cosyntropin (Cortrosyn) stimulation test
Corticotropin test
ACTH stim test
ACTH challenge test
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This article waslast modified on March 25, 2021.
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At a Glance
Why get tested?

To help diagnose primary adrenal insufficiency (Addison disease) and to detect conditions affecting the pituitary gland (secondary adrenal insufficiency)

When to get tested?

When your cortisol level is low and/or your healthcare provider suspects that your adrenal glands are not producing enough of the hormone cortisol or that the pituitary gland is not producing enough adrenocorticotropic hormone (ACTH)

Sample required?

An initial blood sample is collected and then a small amount of a synthetic fragment of ACTH is injected into a muscle (IM) or into a vein (intravenously). Additional blood samples are taken 30 minutes and/or 60 minutes after the intravenous injection.

Test Preparation Needed?

Follow directions given to you by your healthcare practitioner. In some cases, you may be instructed to refrain from taking certain medications on the day of testing.

What is being tested?

Although the ACTH stimulation test name sounds as though it would measure adrenocorticotropic hormone (ACTH), it is actually a procedure used to evaluate cortisol production and to help diagnose adrenal insufficiency.

Cortisol is a hormone produced by two small glands that sit atop the kidneys called the adrenal glands. Cortisol plays a role in the metabolism of proteins, lipids, and carbohydrates. It affects blood glucose levels, helps maintain blood pressure, and helps regulate the immune system. Normally, the level of cortisol in the blood rises and falls in a consistent pattern throughout the day (called diurnal variation), peaking shortly after waking, then declining gradually to its lowest level at bedtime.

Production of cortisol by the adrenal glands is regulated by a negative feedback system involving the hypothalamus in the brain and the pituitary gland, a small organ located below the brain. Normally, in a healthy person:

  • When the cortisol level falls, the hypothalamus responds by releasing corticotropin-releasing hormone (CRH).
  • CRH signals the pituitary gland to produce ACTH.
  • ACTH then signals the adrenal glands to produce and release cortisol.
  • As the cortisol level rises, the hypothalamus decreases CRH production, the pituitary reduces ACTH production, and the adrenal glands decrease cortisol production.

In order for appropriate amounts of cortisol to be made, the hypothalamus, the pituitary, and the adrenal glands must be functioning and communicating with each other properly.

Decreased cortisol levels may be seen with:

  • Underactive or damaged adrenal glands (adrenal insufficiency) that limit cortisol production; this is referred to as primary adrenal insufficiency and is also known as Addison disease.
  • An underactive pituitary gland or a pituitary gland tumor that inhibits ACTH production; this is known as secondary adrenal insufficiency.
  • Treatment utilizing glucocorticoids, such as dexamethasone and prednisone.

If you have a cortisol test done and the result is low, your healthcare practitioner may do an ACTH stimulation test to help confirm the findings and to help determine its cause.

The most common ACTH stimulation test is the short or rapid test. For this test:

  • Your blood is drawn for an initial, baseline level (pre-stimulation).
  • You are given an injection of a manufactured fragment of ACTH (cosyntropin or tetracosactide). The manufactured fragment may be injected into a muscle or vein. When the manufactured ACTH fragment is administered, it acts like the body's own ACTH and stimulates the adrenal glands to produce cortisol.
  • Your blood is drawn again after a specified amount of time (30 minutes and/or 60 minutes).
  • The cortisol level is measured in both the first (baseline) and subsequent samples.

2016 guidelines from the Endocrine Society consider this the best test to establish a diagnosis of primary adrenal insufficiency.

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Common Questions
View Sources

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Annane, D. et. al. (2017). Guidelines for the Diagnosis and Management of Critical Illness-Related Corticosteroid Insufficiency (CIRCI) in Critically Ill Patients (Part I) Society of Critical Care Medicine (SCCM) and European Society of Intensive Care Medicine (ESICM) 2017. Medscape Critical Care Medicine from Crit Care Med. 2017;45(12):2078-2088. Available online at Accessed May 2019.

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