A blood sample is 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.
Exogenous steroids (glucocorticoids) should be stopped at least 24 hours before the test e.g. prednisolone, 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 (alternative forms of contraception should be used). Please discuss with your healthcare professional prior to the test being performed.
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 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. A baseline blood sample is taken through the cannula before the test. A solution containing synacthen is then injected into the vein. After 30 minutes a second sample of blood is taken. Cortisol is measured in the blood samples.
Is any test preparation needed to ensure the quality of the sample?
Exogenous steroids (glucocorticoids) should be stopped at least 24 hours before the test e.g. prednisolone, and inhaled steroids should not be taken the morning of the test. Those taking oestrogen replacement of the oral contraceptive containing oestrogen should ideally stop 6 weeks prior to the test (alternative forms 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.
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. 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 gland is normally stimulated to work by ACTH, the hormone that synacthen mimics, 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 assess pituitary function indirectly and is the mainstay of monitoring patients post pituitary surgery.
When is it requested?
When a doctor suspects the adrenal glands are not working properly and that the patient may have Addison’s disease. The most common cause of this is due to ‘exogenous steroid use’ i.e. suppression of the gland after high dose steroids have been prescribed for another condition.
Assessment or monitoring of pituitary function e.g. if a pituitary tumour is found, after brain surgery or brain radiotherapy.
What does the test result mean?
A normal rise in cortisol following administration of synacthen, means the adrenal glands (and pituitary) are working properly and you don’t have Addison’s 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 may have Addison’s disease (or pituitary abnormality). The expected rise in cortisol concentration post administration of synacthen depends on the assay used in the laboratory doing the analysis. Therefore results that may be normalat 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.
Is there anything else I should know?
- Side effects – Very rarely 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. Any injection or blood test may be associated with pain at the time and possible bruising afterwards.
What happens if my test is abnormal?
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 irrespective of the cause.