There are 2 common tests that can be performed to figure out whether your child is sensitised to some allergen. These are as follows:
1) Skin Prick Test (SPT) - we place a drop of the relevant allergen on your child’s skin (usually their forearm or upper back). The skin under the drop of allergen is then pricked with a lancet (a metal stick with a small point on the end that scratches the top layer of the skin). By doing this, the allergen gets under the skin surface. We will then wipe away the drop. We can test for several allergens at your appointment. We will repeat the same process for each allergen and make a different mark on your child’s skin with a washable pen for each test. This means we can identify the different allergen tests. After 15 minutes, we will check your child’s skin for a reaction. There are two types of reaction:
- Positive reaction – the skin under the drop of allergen becomes red and itchy. A white, raised swelling called a wheal is surrounded by a red area. This takes about 15 minutes to reach a maximum size and then fades after a few hours. We measure this swelling with a tape measure. If the swelling is above a certain size, this means that your child is likely to be allergic to the substance in the solution.
- Negative reaction – the skin under the drop of allergen remains normal. This means that your child is not likely to be allergic to the substance in the solution.
CAUTION - If your child is taking antihistamine tablets such as chlorphenamine, cetirizine (Zirtek®), or loratadine (Clarityn®), he/she needs to stop taking them at least 4 days before their appointment.
We can perform skin prick tests for a range of foods such as: milk ,egg, soya, multiple nuts, common fish, shell fish, wheat and a range of meat.
We can also test for a wide range of aeroallergens, for example grass and tree pollen, house dust mites, cockroach and pet animals .
If you think your child may have had an allergic reaction to any other food, you can bring a small piece of it with you to the clinic. SPT to fruits is ideally done with a whole piece of the fruit itself.
2) Allergen -Specific IgE blood test -immune system of an allergic person produces antibodies called immunoglobulin E (IgE) to a specific allergen. IgE antibodies are unique to each allergen (for example, IgE produced in response to peanut differs from IgE produced to grass pollen) hence, checking for specific IgE antibodies in the blood can help determine if an allergy is present.
Elevated levels of specific IgE antibodies may mean an allergy is present. However, the amount of IgE doesn't necessarily predict the severity of the reaction. We interpret the results in comparison with your child's symptoms and other allergy tests (SPT).