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Allergy testing

The skin test panels cover all the common food and environmental allergens. If you believe your child may be allergic to an unusual food or to a fruit or vegetable, then it is very helpful if you could bring these with you as we can use it to do an allergy test.

It is important that antihistamines are stopped for at least four days prior to the consultation as antihistamines may interfere with the results of the skin tests.

As well as skin tests, our specialist nurses may perform lung function tests, or take the opportunity to revise your asthma inhaler or epipen skills.

After the testing, the results will be passed to the doctor who saw you and you will have the opportunity to discuss them. You will also have the opportunity to spend time with one of our specialist children's dietitians, if needed.

Allergy testing can slow the clinic appointments down (as time is needed for the tests to react). Your journey through our department is likely to include time with our doctors, nurses and dieticians, with diagnostic skin tests for most children. Therefore, please allow at least two hours for your child’s visit.

We provide a variety of toys and books for your child to enjoy while they are waiting. You can also bring any toys or electrical devices which your child would like, to occupy them while they wait.

We have wall displays and information leaflets, which you may find interesting to read and gain further information about allergic disease. There is also free internet access available by logging on to the NHS WiFi network on your device. Please note that some internet content will be automatically blocked.

Please bring any medicines that your child is taking with you to the clinic. If your child has been referred because of a possible reaction to a medicine or anaesthetic, please bring along a summary of the medicines, which were given at the time of the reaction. This will help us in planning the most appropriate testing to be performed.

Types of tests

There are three types of allergy tests - skin prick test, specific IgE blood tests (previously called RAST tests) and atopy patch tests. Your consultant will discuss with you which tests are most appropriate.

The three allergy tests

Skin prick test

These are the most common test we do in our clinic. They help to tell us whether a child is at risk of an immediate allergy to the substance being tested.

It is important that antihistamines are stopped for at least four days before the consultation as antihistamines may interfere with the results of the skin tests.

Skin tests are performed by our nurse specialists. Drops of allergen extract are placed on the child’s forearm and then a small pin is pricked onto the skin. The test is not painful but may cause some itchiness. If the test is positive, then an itchy spot or wheal will appear after 20 minutes. The size of the wheal is measured and recorded and then passed to the doctor for interpretation.

Skin tests need expert interpretation to be useful. The diagnosis of an allergy needs both a careful consideration of the patient’s symptoms as well as the test results.

Find out more in our patient information leaflet Skin prick testing (PDF 89Kb).

Specific IgE blood tests

Sometimes, it is not possible to do skin tests on a child, for example if they have had antihistamines in the days before the test. In these cases, a blood test can provide similar information. If your child wishes, we can put on a anaesthetic cream on his or her skin – this will temporarily numb the skin and help to reduce the discomfort of the blood test.

Lung function testing

These tests can help assess if a child has asthma and if they do, how well controlled it is. It simply involves blowing into a special tube, attached to a computer. Unfortunately, children under six years of age tend not to be able to master the technique to use this equipment.






Tel: 020 7188 3300

Opening hours: Monday-Friday, 9am-5pm

How to find us

Children's Allergy Service
Second Floor, Staircase B, South Wing
St Thomas' Hospital
Westminster Bridge Road
London SE1 7EH

This department is only accessible via lift/staircase B.

Map of Second Floor, South Wing, St Thomas' Hospital

©  Guy's and St Thomas' NHS Foundation Trust.
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