Short Synacthen Test to Check Adrenal Gland Function

A synacthen test is done to check adrenal gland function. It helps to determine if your body is producing enough cortisol, a steroid hormone.

This article provides some information about a short synacthen test as a general guide. The conduct of the tests and arrangements may vary among various hospitals. It is advisable to always follow your doctor’s instructions about the test.

What Is a Short Synacthen Test and Why Do I Need It?

A short synacthen test helps evaluate your adrenal gland function with regards to hormone production, particularly cortisol, a natural steroid hormone. Cortisol is a hormone that enables the body to respond to illness and stress. It also regulates immune system function as well as blood sugar and blood pressure levels.

The production of cortisol in your body is controlled by a tiny gland under the brain called the pituitary gland. Low cortisol levels may be caused by a either pituitary gland or adrenal gland dysfunction.

Adrenal failure to produce adequate levels of cortisol leads to Addison’s disease. If your doctor suspects you have Addison's disease, a special test called short synacthen test is done to confirm the diagnosis. It involves stimulating the adrenal gland to produce cortisol by injecting a drug (Synacthen), which is similar to a hormone (ACTH) produced by the pituitary gland that normally stimulates the adrenal gland. Normal adrenal gland function is shown by the rise in cortisol levels after drug injection. However, if you have Addison's disease, your blood cortisol levels will not rise after the injection.

How to Prepare for a Short Synacthen Test

There’s nothing much that you need to prepare especially for the test, but still, there’re some notes you need to keep in mind:

On the morning of your synacthen test, do not take prednisolone, hydrocortisone, or other steroids. If you are being treated with high doses of steroids a week before your test, ask your doctor for advice.

You will be allowed to take your medications after the test, so bring them with you on the day of your appointment.

What Will Happen During a Short Synacthen Test?

You should go to the testing center early on the date of your appointment. You will be asked to lie down on a bed throughout the whole test. A small needle (cannula) with a tube attached will be used to take blood samples from a vein in your arm.

After taking the first (baseline) blood sample, you will receive an injection of synthetic hormone (ACTH) into your arm or thigh muscle. Another blood sample will be taken from the inserted cannula at 30 minutes and one more at one hour. The cannula is removed when the short synacthen test is completed, and you will be allowed to go home.

How to Interpret the Test Results

The following is a brief explanation of what your results may mean. Talk to your doctor about your results to fully understand your condition and the possible treatment you might need.

1. Normal Results

A normal test result from a short synacthen test will show a serum cortisol concentration that is greater than 540 nmol/Lat 30 minutes. This increase in cortisol at 30 minutes above the initial level is an indication of your adrenal reserve, while a low absolute level indicates adrenal sufficiency.

Remember, however, that the interpretation of your results must take into consideration your stress level and the time when the test was taken. Stress increases the cortisol production of your adrenal gland, so your basal cortisol may be greater than 540 nmol/L, which is followed by a very small increase after 30 minutes. However, this does not mean that you have adrenal insufficiency. When an increase in the basal level is not observed, cortisol levels at 30 minutes will rise by at least 200 nmol/L.

Normal results exclude the diagnosis of primary adrenocortical insufficiency, but this does not necessarily mean that you do not have ACTH deficiency. You may have a partial ACTH deficiency even if you have a normal or a reduced response to a short synacthen test.

2. Interpretations of a Decreased Response

If you had a decreased response in a short synacthen test, normally there’re 3 possible interpretations, which are:

  • Primary adrenal failure (ex. Addison’s disease). Test results will show a low level of baseline cortisol with no response or little rise after injection of synthetic ACTH.
  • Adrenal atrophy (adrenal gland shrinkage), due to prolonged deficiency in ACTH.
  • Adrenal atrophy, due to long term therapy with steroids.

3. Other Factors to Consider

  • Females usually have a small yet significantly greater cortisol response value compared to males.
  • Age does not affect the synacthen test results.
  • The interpretation of test results does not apply to women who are using oral contraceptives.
  • The response to a synacthen test is not affected by obesity.
  • An abnormal response to Synacthen may need further investigation.
  • It is difficult to make a reliable assessment of the synacthen test results in patients who are severely ill because of significantly low levels of a protein called cortisol-binding globulin (CBG), which decline substantially during the acute phase. 80% of total cortisol is bound to the protein, and CBG variations significantly affect total cortisol levels, which could affect the interpretation of the results.

Anyway, the short synacthen test may be repeated in three months when necessary. Certain drugs, especially steroids like prednisolone and hydrocortisone, may interfere with the results of your test. Tell your doctor about all the medications you are using, including inhaled and topical steroids.

If you are diagnosed with hypoadrenalism, an ACTH sample must be taken before you starting the steroid therapy. A referral to an endocrinologist must be made for proper treatment.