ACTH Suppression- Pathology

ACTH Suppression Test

An ACTH suppression test, also known as a dexamethasone suppression test or cortisol suppression test, helps diagnose Cushing syndrome. Cushing syndrome, also called Cushing's syndrome, may be suspected if your cortisol level is unusually high. Cortisol is a glucocorticoid hormone that is produced by the adrenal glands. 

There are two kinds of dexamethasone suppression tests; low dose and high dose. If your body is producing excessive ACTH, the low-dose dexamethasone suppression test can help identify this issue. The high-dose test can assist in identifying whether the pituitary gland is the root cause (like in Cushing disease).

Why Is The Test Performed?

A dexamethasone suppression test determines how taking dexamethasone affects your cortisol levels. Dexamethasone is a synthetic corticosteroid that resembles the hormones your adrenal glands naturally produce. If your body does not produce enough of the natural chemical, it is necessary to supplement it. Additionally, it may be used as an anti-inflammatory drug to treat arthritic conditions as well as specific blood, renal, and eye conditions.

Our body has two adrenal glands, one located on the top of each kidney. In addition to cortisol, they also produce steroid hormones like:

  • Androgens, the male sex hormones
  • Cortisol
  • Norepinephrine
  • Epinephrine

The test also assesses how well the adrenal glands react to the adrenocorticotropic hormone (ACTH). ACTH is a hormone synthesized by the pituitary gland in the brain. It performs a variety of tasks, one of which is corticosteroid production. Cushing syndrome can be brought on by excessive ACTH. In a healthy individual, the adrenal glands produce less cortisol as the pituitary glands produce less ACTH. Dexamethasone should reduce ACTH production, which then would lead to a reduction in cortisol production.

Your doctor might advise a dexamethasone suppression test if you are currently taking the corticosteroid drug dexamethasone. This test will see how the drug is influencing your blood cortisol levels.

Among other disorders, dexamethasone reduces inflammation brought on by severe allergies and rheumatoid arthritis. In addition, dexamethasone, which is highly similar to cortisol, should decrease the amount of ACTH produced in your bloodstream when you take it. After taking a dose of dexamethasone, a high cortisol level is a marker of an abnormal condition.

How Is The Test Performed?

Both the low-dose and the high-dose tests can be completed in one sitting or over the course of three days. The three-day test is the standard test for both. Your medical professional will administer a dose of dexamethasone throughout both types of tests, and they will then check your cortisol levels. A blood sample is also required.

Taking A Blood Sample

A vein on the back of your hand or inside your lower arm is used to draw blood. Your healthcare professional will first swab the area with an antiseptic. The vein may be made more noticeable by using an elastic band around the top of your arm. Next, your healthcare practitioner will place a tiny needle into the vein and draw blood into a tube that is attached to the needle. The band is removed to stop further bleeding, and gauze is put into the area.

Administering The Test

The test can be administered in the following ways:

Common Tests

1. Low-dose overnight dexamethasone suppression test

One milligram (mg) of dexamethasone will be administered at 11 p.m., and your blood will be drawn the following morning at 8 a.m. for a cortisol measurement.

2. High-dose overnight dexamethasone suppression test

The provider will check your cortisol levels on the morning of the test. At 11 p.m., 8 mg of dexamethasone will be administered. Then, the following morning at 8 a.m., your blood sample is taken to measure your cortisol levels.

Rare Tests

1. Standard low-dose dexamethasone suppression test

Urine is collected over the course of three days and stored in 24-hour collection containers to measure cortisol. On day 2, you will take a low dose of dexamethasone (0.5 mg) orally six times daily for 48 hours.

2. Standard high-dose dexamethasone suppression test

Urine is collected over the course of three days and held in 24-hour collection containers to assess cortisol in the standard high-dose method. On day 2, a high dose of dexamethasone (2 mg) will be given orally every six hours for 48 hours.

Carefully read and adhere to the instructions. The most frequent cause of an abnormal test result is when instructions are not followed properly.

How To Prepare For The Test?

Before the test, you may be instructed to avoid using specific prescription medications that may alter the results. These consist of the following:

  • Contraceptive pills
  • Phenytoin, a drug used to treat seizures
  • Barbiturate
  • Tetracycline, a kind of antibiotic
  • Estrogens
  • Corticosteroids
  • Spironolactone, a medication for kidney issues, ascites, and congestive cirrhosis

How Will The Test Feel?

You may experience moderate pain when the needle is inserted to draw blood. Sometimes it may just feel like a sting or prick. There can be some pain or minor bruises afterward, but this quickly disappears.

Interpreting The Results

Normal values

The cortisol levels should drop after receiving dexamethasone.

1. Overnight test:

Low dose - Plasma cortisol levels are less than 50 nanomoles per liter (nmol/L) or 1.8 mcg/dL at 8 a.m.

High dose - Greater than 50% reduction in plasma cortisol

2. Standard test:

Low dose - Less than 10 mcg/day or 280 nmol/L of urinary-free cortisol on day three.

High dose - Greater than 90% reduction in urinary free cortisol

Different laboratories may have slightly different normal value ranges. In addition, some laboratories may test various specimens or utilize other measurements. Ask your doctor what your particular test results signify.

What do abnormal results mean?

You may have abnormal cortisol release (Cushing syndrome) if you respond abnormally to the low-dose test. This might be because of the following:

  • Cortisol-producing adrenal tumor
  • A pituitary tumor that produces ACTH
  • Body tumor that produces ACTH (ectopic Cushing syndrome)

A pituitary cause (Cushing disease) can be distinguished from other reasons using the high-dose test. In addition, an ACTH blood test can also help find the cause of elevated cortisol.

The abnormal result varies depending on the underlying condition causing the issue.

1. Cushing syndrome caused by an adrenal tumor

  • Low-dose test - no drop in blood cortisol
  • ACTH level - low
  • The high-dose test is typically not required

2. Ectopic Cushing's disease

  • Low-dose test - no drop in blood cortisol
  • ACTH level - high
  • High-dose test - no drop in blood cortisol

3. A pituitary tumor that causes Cushing syndrome (Cushing disease)

  • Low-dose test - no drop in blood cortisol
  • High-dose test - expected decrease in blood cortisol

Numerous factors, including various medications, depression, obesity, and stress, might result in false test findings. In addition, women experience false results more frequently than men.

The blood dexamethasone level and cortisol level are often checked in the morning. The dexamethasone level must be greater than 200 nanograms per deciliter (ng/dL) or 4.5 nanomoles per liter (nmol/L) for the test result to be accurate. Therefore, lower dexamethasone concentrations may result in a false-positive test result.

Risks Associated With The Test

There is minimal risk with having your blood drawn. The size of the veins and arteries varies between different parts of the body. Also, it varies from patient to patient. It could be more challenging to draw blood from some people compared to others.

Having blood drawn carries a few minor additional risks, which could include:

  • Excessive bleeding
  • Several punctures to identify veins
  • Fainting or experiencing dizziness
  • Hematoma (blood accumulating under the skin)
  • Infection (a minor possibility any time the skin is broken)

In rare instances, swelling in the vein may develop after blood is drawn. This is known as phlebitis. Applying warm compresses in the affected area multiple times a day helps to treat this issue.

In case you have a bleeding disorder or are taking blood thinners like aspirin or warfarin (Coumadin), ongoing bleeding could be a problem.

Follow-up After The Test

Your healthcare provider could advise additional tests to identify Cushing syndrome, even if the result is abnormally high. If this disease is identified, you will be prescribed the right drugs to reduce your elevated cortisol levels.

Your doctor will suggest more tests to identify the type of cancer and the best course of therapy if cancer is the cause of your elevated cortisol levels. However, your healthcare provider might recommend a different treatment plan if other illnesses are linked to your high cortisol levels.


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