Skin-prick testing

What is skin-prick testing for?

It can help to assess if you may be allergic to something. This could be an allergy to something you are breathing in or something you are eating.

What does the test involve?

A small droplet of fluid containing the substance you might be allergic to is pricked onto your skin. This could be done on your arm, thigh or back. The droplet is applied to the top layer of the skin with a very fine needle, so it is usually only felt as a slight prick or gentle scratch and rarely draws blood.  After 10-15 minutes the test area is examined. Positive results are when the prick site has come up in a wheal (a raised red bump). The doctor will also do the test with salt water which should not react and with another substance that should definitely react. This is to check that the tests are working and the results are reliable.

Is there anything I need to do before the test?

You may need to temporarily stop some medications before your skin prick test as they can interfere with the results. Medications that can affect results include steroid tablets and steroid creams (steroid inhalers are not a problem) and some anti-allergy medications, like antihistamines. Your doctor will advise you. Check if you have any concerns. Do not stop any medication without advice. You should be feeling well on the day of the test and not have any other skin conditions that might make it hard to interpret the results.

What are the advantages and disadvantages of this test?

Skin-prick testing is quick and easy to perform and the results are immediate. It is very safe but there is a chance you could get an irritating reaction at the site of the test that could last a few hours. There is a small chance that you could have a reaction that could make you feel unwell or, in extreme circumstances, an anaphylactic reaction (a very severe allergic reaction affecting the whole body). This is very rare indeed.

What happens after the test?

 The results will be available immediately. Your doctor will interpret the result in the context of your history. Sometimes it is not straightforward and a positive skin reaction does not always mean an allergy is certain – your doctor can explain this further.