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There are various types of allergy tests, including skin prick tests and blood tests. Your consultant or nurse specialist will decide which tests your child needs, based on their history. An allergen is the name given to the substance causing an allergy, for example a food or pollen.
Skin prick testing
Skin prick testing is safe and simple, and helps to show if your child is at risk of an immediate allergy. One of our specially trained children's nurses will do the test.
The nurse will mark your child's forearm using a special pen and place a small droplet of each allergen solution next to it. Then a small pin is used to scratch the skin through each droplet. It is a bit like being pressed with a ballpoint pen; your child will feel it and it may cause some itchiness.
After the test, the solutions are wiped off. We can read the results after 15 minutes. If the test is positive, a white itchy spot or wheal (a white raised lump) will appear. The size of the wheal is measured and recorded, so a doctor can interpret it.
The size of the wheal doesn't indicate the severity of the symptoms. The test tells us which allergens may be causing your child's symptoms. Skin prick testing is a very safe procedure, however if a reaction occurs, for example itchy skin or swelling, we will give your child oral antihistamine immediately.
After the allergy test, the doctor or nurse will give you advice and information based on your child's test results.
Antihistamines and skin prick testing
It is important to stop all antihistamines before the skin prick test as they will interfere with the results. Please stop all medicines containing antihistamine four days before your allergy clinic appointment.
However, if your child really needs to take them, then give them the antihistamine medicine. If your are in doubt as to whether the medicine your child is taking contains antihistamine, please contact us on 023 8120 4075 a week before their appointment for advice.
Specific IgE blood tests
Sometimes, it is not possible to do skin prick tests on a child, for example if they have taken antihistamines in the days before the test or if they have bad eczema. In these cases, a blood test can provide a similar information because it is possible to detect an allergy antibody to a food or pollen in the blood; this is known as Specific IgE.
If you or your child wishes, we can use an anaesthetic cream, which will numb the skin for a while and help to reduce the discomfort of the blood test. Very occasionally, a bruise may appear in the area where the blood has just been taken from.
Lung function tests
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.
Food challenges are performed in hospital as it is the safest way of finding out how your child reacts to a food.
Types of food challenges:
Diagnostic - sometimes it is unclear if a food is causing the reaction, this needs to be confirmed.
Resolution - to see if a food allergy has been outgrown and if the food can be tolerated and reintroduced into your child's diet.
Demonstration - for teenagers who have never been exposed or were too young to remember an allergic reaction. This is not to provoke a severe reaction but to demonstrate what the early stages of an allergic reaction feel like and how they respond to treatment.