Synacthen Test

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.