Skin prick allergy testing for respiratory (aeroallergen) allergies
Checking for allergies using a skin prick test is a safe way of identifying any substances that cause an allergic reaction when your child is exposed to them.
This page from Great Ormond Street Hospital (GOSH) describes what to expect when your child has a skin prick allergy test in the Lung Function unit and the next steps needed, depending on the results of the test.
What is an allergy?
An allergy occurs when the immune system sees a harmless substance as harmful and reacts to it, releasing a number of chemicals into the bloodstream. The substance causing a reaction is called an allergen. The most common aeroallergens include pollen, mould and animal.
An allergic reaction to a substance triggers the immune system to release antibodies to fight off the ‘invader’. In turn, this releases certain chemicals, such as histamine, into the bloodstream. It is these substances that cause the symptoms of an allergic reaction.
What are the symptoms of an allergic reaction?
A reaction cannot occur the first time someone comes into contact with an allergen. The immune system has to learn and recognise an allergen to have a reaction. The reaction will vary depending on how a person came into contact with the allergen too. For instance, skin contact can cause rashes and inhaled (breathed in) contact can cause wheezing and a runny nose.
Allergic reactions can be mild to severe. Signs of a mild allergic reaction include skin rashes and itching, high temperature, shivering, redness of the face, a feeling of dizziness or a headache. Signs of a severe allergic reaction include any of the above, as well as shortness of breath or chest pain.
What happens before a skin prick allergy test?
You will already have received information about how to prepare your child for the test in a letter or discussed it with your referring doctor.
On the day, the Physiologist will explain the test in more detail. We will ask for your permission (consent) to perform the test. If your child has any medical problems, please tell us about these.
Your child should stop taking anti-histamine medicine seven days before the test. If your child has a reaction in the days leading up to the test, you should give them anti-histamine as usual but please telephone us to let us know. We may have to postpone the test for a few days.
We will confirm any other medicines that may need to be stopped before you come to GOSH. You should also avoid putting any lotion or cream on your child’s arms as this may alter the test results.
The person bringing your child for the test should have ‘Parental Responsibility’ for them. Parental Responsibility refers to the individual who has legal rights, responsibilities, duties, power and authority to make decisions for a child. If the person bringing your child does not have Parental Responsibility, we may have to cancel the test.
What does the skin prick allergy test involve?
To carry out the skin prick test, 16 allergens including a positive control, a negative control, and other aeroallergens like pollens, moulds, dust mites, and animal fur are placed on your child’s arm.
This is done with an applicator which applies eight of the allergens at once, both arms are used for application. The applicators are placed in the allergen tray and then make a small prick to the upper skin layer.
The application sites will then be dried, the reactions will take 20 minutes to develop during this time we ask you to make sure your child avoids scratching. The positive control is histamine, which everyone will react to, this is normally seen by a raised red bump known as a wheal. It may also be itchy.
After a wait of 20 minutes, the Physiologist will measure the reaction to each of the allergens (if any). Your child can then wash their arm to ease the itching. The itching should get better and the reaction will usually go down after an hour. The Physiologist will tell you what to do if the irritation continues for longer than an hour.
Are there any risks?
Skin prick allergy tests carried out in hospital are very safe – the Physiologists are experienced in carrying out the test.
Skin prick tests are good at identifying most allergens, but other tests might be needed to check your child’s reaction to medicines or food. Please feel free to bring along something that might help in distracting your child.
Getting the results
The report is uploaded onto our electronic patient record system for your doctor to view. If you are seeing your doctor in clinic or later that day, they will go through the results with you.
If you are not seeing the doctor that day, they will be able to view your test results and contact you if there is anything that needs to be addressed before your next appointment.