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What is being tested?

Synacthen is a manufactured drug that acts like adrenocorticotrophic hormone (ACTH) by stimulating the adrenal gland to produce more cortisol. By measuring the rise in cortisol in the blood the doctor can see if the adrenal glands are secreting normal amounts of cortisol.

How is it used?

The test is used to see if the adrenal glands are producing normal amounts of cortisol. When the adrenal does not produce enough cortisol and aldosterone the patient can feel tired, lethargic, sick and lose weight and may become dangerously ill. Synacthen stimulates the adrenal glands to produce these steroids. If the adrenal glands are not working properly then the rise in cortisol after the injection of synacthen is either low or absent.

The adrenal gland is normally stimulated to work by ACTH, the hormone produced by the pituitary gland that Synacthen mimics. If the pituitary is not working for more than a few weeks the adrenal glands will shrink and not be able to respond to the Synacthen. Therefore the Synacthen test can also be used to assess pituitary function.

When is it requested?

When the doctor suspects the adrenal glands are not working properly and that the patient may have Addison’s disease.

When the doctor wants to assess pituitary function e.g. if a pituitary tumour is found on an X-ray or after brain radiotherapy.

What does the result mean?

A normal rise in cortisol means the adrenal and pituitary glands are working properly and you don’t have Addison’s or pituitary disease. The laboratory and doctors will have established what a normal cortisol rise is. If the rise in cortisol is low or absent it suggests that the patient has Addison’s disease or pituitary ACTH deficiency.

Is there anything else I should know?

  • Side effects – Some patients experience slight feeling of sickness, flushing of their face and a faster heartbeat. These are only brief and will have disappeared by the end of the test.
  • Asthma – You should tell the nurse or doctor if you suffer with asthma or a chest condition for which you use an inhaler.
  • Allergies – tell the doctor or nurse if you have any allergies.

Common questions

  • What happens if my test is abnormal?

The doctor will probably take more blood for other tests to find out whether it is the adrenal or pituitary gland that is not working properly and why. If your result is very abnormal the doctor will give you steroids to replace those your body is not producing.

Last Updated: Thursday, 1st June 2023

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