How to Interpret the ACTH Stimulation Test

Instructor: Jason Lulejian

Jason has taught medicine and has a Medical Degree from Western University of Health Sciences

First this lesson will review how and why an ACTH stimulation test is performed. Then, interpretations of high or low values, as well as limitations of the test will be discussed.

Review of Adrenal Glands

Ever heard of the 'stress hormone'? It's a signal in your body that prepares you to deal with stress, like in fight or flight situations. However, we hear about it mostly because of chronic stress, where the hormone gets too abundant in our bodies and starts wreaking havoc.

The adrenal glands are two small, fatty glands that sit on top of the kidneys. Their primary purpose is to secrete different hormones to help regulate the body's most critical functions. These little glands are famously known for producing adrenaline, but they also make hormones that regulate our blood pressure, fat storage, and blood sugars. These are known as corticosteroids like cortisol, aka 'the stress hormone'.

The adrenal glands receive signals to make this hormone from the pituitary gland in the form of another hormone, ACTH (Adrenocorticotrophic releasing hormone), which receives signals from the hypothalamus, a part of the brain. So, the hypothalamus sends signals to the pituitary gland, which sends ACTH to the adrenal gland, which then makes corticosteroids.

These two glands coordinate with each other to help keep us alive and healthy through a variety of situations, and to protect our bodies from becoming swamped with too many hormones.

But like so many bodily processes, things can go wrong. In diagnosing many diseases of the adrenal glands, doctors use an ACTH stimulation test which studies the Hypothalamic-Pituitary-Adrenal (HPA) system, one of the primary drivers of corticosteroid production. Before we get into how to interpret results, let's review the test itself.

Basic Concepts of ACTH Stimulation Testing

The ACTH stimulation test relies on negative feedback, where some kind of stimulus is used to get a reaction from the body natural regulation of itself to maintain ideal levels. It's sort of the scientific equivalent of poking something with a stick to see what it does to compensate. It's provoking a response as a way of testing out function.

The Hypothalamic-Pituitary-Adrenal (HPA) system
HPA axis and negative feedback

The ACTH stimulation test primarily uses the synthetic form of ACTH, which is injected into the patient during the test. The expectation is that the body will react to the additional ACTH by producing cortisol from the adrenal cortex. After about an hour, the levels of cortisol and a related hormone in the adrenal glands, aldosterone, are measured in the blood or urine.

Test Results

Normal

ACTH stimulates the production of cortisol by acting on the adrenal cortex. If the patient is properly prepared for the procedure, you can expect to see a rise in the blood and urine cortisol content shortly thereafter. The cortisol level should rise above 20 mcg/dl, which would indicate that the adrenal tissue is functional and responsive to ACTH.

This is a lot like nudging someone when they are asleep, you would expect them to wake up, which indicates that they are okay.

Low

However, what happens when this is not true? ACTH should stimulate cortisol production, regardless of the health of the pituitary gland, so if appropriate ACTH was given and there is no rise in cortisol levels, the adrenal cortex is assumed to be the source of disease.

This result narrows the differential diagnoses to diseases such as Addison's disease and adrenal insufficiency, as well as diseases associated with hypocortisolism (low cortisol levels). To continue the analogy, this would be like nudging someone while asleep, but they do not wake up. To many people, this would be a response that would cause concern.

High

Conversely, if the levels of cortisol rise significantly above 20 mcg/dl, the pituitary gland itself may have a disease such as hypopituitarism (low hormone secretion). If the patient has come in with low blood pressure and low blood sugar, these are symptoms of low cortisol. If their cortisol spikes overly high in the ACTH test, it's likely that the issue is coming from the pituitary gland (or further upstream at the hypothalamus).

This would be like our analogy of nudging someone when asleep, only this time the person springs up and slugs you in the face. This would also indicate a problem, but with a different cause.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support