Synacthen test

Investigation Protocol


Diagnosis of Addison’s disease, hypothalamic-pituitary-adrenal axis suppression or congenital adrenal hyperplasia.

Preparation and precautions

This test can be performed at any time of the day and the patient may eat and drink normally.

Patients should be asked to bring in all their medications, including over the counter medicines and creams. Also, check whether they have had any recent joint injections. Usual medications may be taken on the morning of the test, but individuals taking inhaled steroids, topical creams, nasal steroids, inhalers and oral steroids (for example prednisolone, hydrocortisone or dexamethasone) should be discussed first with the referring consultant. Patients taking more than 7.5 mg prednisolone or equivalent are highly likely to be adrenally suppressed, and so the test may not be appropriate or necessary. Patients taking oral steroids must omit them on the morning of the test but bring them with them to take as soon as the test is completed. 

Estrogen containing medications, including the contraceptive pill and hormone replacement therapy, should be stopped for six weeks prior to measuring serum cortisol. This is because estrogen induces cortisol binding globulin and leads to elevations in measured serum cortisol. Procedure

All patients should have had a 9am cortisol taken before the test is arranged. If the level is above 500nmol/l or below 100nmol/l, the test is generally unnecessary and this should be discussed with the referring doctor.


Blood samples can be taken by venepuncture however the patient should be given the option of having an indwelling gauge 20 cannula with a three-way tap.

Using the vacutainer connector system, or a syringe, fill one plain clotted tube for cortisol (and for 17-hydroxyprogesterone where the test is being performed for possible congenital adrenal hyperplasia). Label with patient identification, date and write 0 minutes as time taken. An additional sample should also be taken into an EDTA bottle, centrifuged, separated and plasma frozen and stored in a freezer in case it is required for future ACTH assay.

Inject synacthen 250micrograms intramuscularly.

Take further plain clotted tube blood samples at 30 and 60 minutes after the injection. It is important to clearly mark the patient’s details, date and time of sample on each bottle.

If patient has a cannula, each time samples are taken flush the cannula with 2mls 0.9% sodium chloride and prior to taking blood samples withdraw 2mls and discard to remove the sodium chloride flush.

If cannulated, remove cannula at end of test and patient may then take-omitted medications and go home.

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Patient information sheet

Synacthen test

Your doctor has referred you for a synacthen test. This is to see if your adrenal glands are producing enough cortisol. Cortisol is one of the essential steroid hormones to keep you healthy and people can become quite unwell if levels of this hormone are too low.

Over one hour a total of three samples of blood will be collected. The stimulus for the test is a drug called synacthen, and this is injected into a muscle in your buttock or leg after the first sample of blood has been taken. This drug has few side effects: some patients experience a slight discomfort (like cramp) in the muscle as the injection is being given but this passes after a few minutes. Occasionally people experience a reddening around the site of the injection. Very rarely people with allergies may feel faint.

If you have diabetes, this test might cause a temporary rise in your blood glucose levels after the test for about a day. The nurse looking after you during the test will advise you about what to do if this happens.

You may take your other medication as normal on the day of the test. However, if you are on the contraceptive pill, take hormone replacement therapy, or take any steroids orally, as nasal drops, inhalers, skin creams or have recently had a joint injection, it is important that you inform us before the test date. You can contact us either by writing to the address at the top, or by phoning the number given at the end of this sheet.

The test takes one hour from the time of injection, so please allow at least one and half-hours to be in the unit. You will be resting in a reclining chair and you may eat and drink as normal on the day of the test. You will be offered a drink whilst you are in the unit.

You may wish to bring a book or magazine to read. We do have a radio, or you can access Patientline; alternatively you may like to bring your own personal radio/cd player (please bring your own headphones). You may bring someone to stay with you during the test but there is not enough space for more than one person.

Children are discouraged, as this can be disruptive to other patients. However, if this poses a particular problem for you please discuss this with the senior nurse in the unit. You should be able to undertake normal activities after the test is finished and it should not interfere with your ability to drive home. 

If you have queries about the test, please contact:

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