How is it assessed?

The main principle in diagnosis of allergy is that the clinical history is the most important factor and any test result should be interpreted in the light of this. Test results do not give any indication of the risk of anaphylaxis, they can only confirm or exclude the causal allergen. The opinion of the Consultant Allergist on the meaning of the test results and the risk of anaphylaxis should always be followed. There are two main investigations for IgE mediated allergy in children and these are skin prick testing and blood tests.

Skin prick testing

In this test drops of diluted allergen are placed on to the arm and the skin pricked through the drop. This exposes the allergen to the immune system. A positive result is indicated by swelling of the skin around the skin prick. The area of swelling is called a wheal. Skin prick testing is a very good way of ruling out allergy as a cause for symptoms. Positive results are not always associated with allergic symptoms and the view of the allergist reporting the skin prick test result is the best guide to interpretation of the test results.

Blood tests

The main test used is called ‘specific IgE’ this measures the amount of IgE that reacts with a particular allergen e.g. peanut. These tests are more commonly available, but are less accurate than skin prick tests.

Food challenge testing

This test involves eating the suspect food in increasing amounts, usually to exclude an allergy. This may be recommended in circumstances where a food allergy is suggested by the history, but allergy tests are negative. Depending on medical judgement this may take place at home, under guidance from the doctor, or in hospital under direct supervision. It is commonly used to demonstrate resolution of the common food allergies of infancy (e.g. egg and cow milk).

Alternative allergy testing

Children at risk of anaphylaxis will have had allergy testing using one or a combination of the above tests to diagnose their allergy. The GP should be able to confirm the presence of allergy and how and by whom it was diagnosed.

A whole industry of private allergy tests has grown up. They can be bought at health shops and over the internet. Examples include Vega testing, kinesiology, hair analysis and alternative blood tests. None of these test results constitute evidence of allergy and any results of such tests should be ignored.

The role of the GP, paediatrician and allergist

It is quite common for children even with severe or multiple allergies to visit the allergy specialist only once for diagnosis and receive all of their future care through the GP or paediatrician. Some allergy specialists will review the child regularly but infrequently, e.g. yearly.