Synacthen Test
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
A Synacthen test measures how well the adrenal glands produce cortisol by taking blood samples before and after an injection of synthetic ACTH (Synacthen), usually given into a vein or muscle. It is used to help diagnose adrenal insufficiency, including conditions such as Addison’s disease or other causes of low cortisol production.
Why get tested?
To help diagnose Addison disease. To assess adrenal and pituitary gland function.
When to get tested?
When a doctor suspects that the adrenal gland is not producing enough cortisol. When a doctor suspects that the pituitary gland is not producing enough adrenocorticotrophic hormone (ACTH).
Sample required?
Two blood samples are collected and then a small amount of synacthen is injected into a vein or muscle. A further blood sample is taken after 30 minutes and/or 60 minutes.
Test preparation needed?
Medications containing steroids (glucocorticoids such as hydrocortisone and prednisolone) should be stopped at least 24 hours before the test, and inhaled steroids should not be taken the morning of the test. Those taking oestrogen replacement, or the oral contraceptive containing oestrogen, should ideally stop 6 weeks prior to the test (different types of contraception should be used). Please discuss with your healthcare professional prior to the test being performed.
What is being tested?
Synacthen is a manufactured drug that acts like ACTH by stimulating the adrenal gland to produce more cortisol. By measuring the rise in cortisol in the blood after synacthen is given the doctor can see if the adrenal glands are secreting normal amounts of cortisol and the pituitary gland normal amounts of ACTH.
How is the sample collected for testing?
A blood sample will be taken and then the synacthen injected, at which point the time is recorded and further sample(s) taken according to the local protocol. Alternatively, a needle or small polystyrene tube (a cannula) with a valve mechanism on the end is put into a vein in your arm. The end is taped to your arm and remains in place during the test. Baseline blood samples are taken through the cannula before the test. A solution containing synacthen is then injected into the vein. After 30 minutes (and/or 60 minutes depending on the local preference), a second sample of blood is taken. Cortisol is measured in each blood sample, and ACTH is sometimes measured in a sample taken before the synacthen is injected if the doctor thinks that this may be needed.
Is any test preparation needed to ensure the quality of the sample?
Medications containing steroids (glucocorticoids such as hydrocortisone and prednisolone) should be stopped at least 24 hours before the test, and inhaled steroids should not be taken the morning of the test. Those taking oestrogen replacement, or the oral contraceptive containing oestrogen, should ideally stop 6 weeks prior to the test ( different types of contraception should be used). The test should not be performed within 6 weeks of pituitary surgery. Smoking and strenuous exercise should be avoided during the test. Please discuss with your healthcare professional prior to the test being performed.
Common questions
The test is used to see if the adrenal glands are producing normal amounts of cortisol. When the adrenal glands do not produce enough cortisol and aldosterone the patient can feel tired, lethargic, sick and lose weight. Synacthen stimulates the adrenal glands to produce cortisol. If the adrenal glands are not working properly then the normal rise in cortisol after the injection of synacthen is either low or absent.
The adrenal glands are normally stimulated to work by ACTH, the hormone that synacthen mimics, which is produced by the pituitary gland. If the pituitary is not working, the adrenal gland will shrink and not be able to respond to the synacthen as long as the ACTH has been absent for more than 6 weeks. Therefore, the SST can be used to test if the pituitary gland is working properly, and is usually used to monitor patients after pituitary surgery.
When a doctor suspects the adrenal glands are not working properly and that the patient may have Addison disease. The most common cause of this is due to ‘exogenous steroid use’. More simply, if medications which contain steroids are taken for too long and/or the dose is too high, this can cause the adrenal glands to stop working properly. This test is to find out if this is a problem or not as extra/different treatment may be required depending on the result.
Testing or monitoring of pituitary function (e.g. if a pituitary tumour is found, after brain surgery or brain radiotherapy).
A normal rise in cortisol following administration of synacthen, means the adrenal glands (and pituitary) are working properly and the patient does not have Addison disease. The laboratory and doctors will already know what a normal cortisol rise should be if the adrenal glands are working properly. If the rise in cortisol is lower than this or is absent, it suggests that the patient may have Addison disease (or pituitary abnormality), and that the patient may require some extra treatment. The expected rise in cortisol concentration after injecting synacthen depends on the particular cortisol test used in the laboratory doing the testing because there are many different versions of test available. Therefore, results that may be normal at one hospital may be considered abnormal at another. Results should only be interpreted according to the local reference ranges and not according to general ones (e.g. found on the internet or in text books). Please discuss with your healthcare professional.
- Side effects – Very rarely some patients experience slight feeling of sickness, flushing of their face and a faster heartbeat. These are usually only brief and often disappear by the end of the test. Any injection or blood test may be associated with pain at the time and possible bruising afterwards.
- 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.
The doctor will probably take more blood for other tests to find out which gland is not working properly and why. Imaging, such as MRI or CT scans, may also be required to look at the glands. If your result is very abnormal the doctor will give you steroids to replace those your body is not producing.