Allergy tests - what you really need to know

Allergies affect 1 in 3 people in the UK and can mean different things to different people, ranging from food aversions to asthma, eczema and severe anaphylactic reactions. Those of us who suffer from hayfever, eczema, asthma or anaphylactic reactions to insect venoms or food allergies, may produce high levels of antibodies known as immunoglobulin E (IgE) to specific allergen triggers. The most common symptom causing allergens are found in dust mites, pet dander and pollens. These allergens are proteins that cause sensitisation and on further exposure can trigger allergy symptoms.

Although a good clinical history can diagnose many common allergies, there are three main types of tests used by doctors that can help identify IgE mediated allergy triggers;

1. Skin prick testing - these tests are only carried out by doctors or nurses with specialist training and facilities, where a drop of allergen solution, extracted from the suspected source such as dust mites, foods or pollens, is scratched into the skin. People with IgE mediated allergies will show an itchy bump and redness surrounding the scratch known as a wheal and flare reaction within minutes.
2. Blood tests that measure the level of allergen specific IgE antibodies to identify sensitisation to specific allergens. These tests are usually performed in hospital labs, although there are some self-testing kits based on the same principles.
3. Total IgE tests - these tests measure the total amount of IgE allergy antibodies in the blood and can give doctors an indication as to whether IgE mediated allergies may be present, but the results are often of little use as many people with allergy symptoms will have a total IgE level in the normal range, whilst some people with very high levels of total IgE antibodies may not have any symptoms.

Allergen specific blood tests, can indicate sensitisation to a particular allergen, but cannot predict with certainty that the allergen will cause symptoms. Nevertheless, allergen specific blood tests can be used to confirm suspicions raised by the patient’s clinical history.

Total IgE self-testing kits that use a low cut-off (<10kU/L IgE) are likely to pick up lots of false positive results and may cause unnecessary worry. On the other hand, test kits with a high cut-off (>150kU/L IgE) may give false negative results to some people who have an allergy but get a negative total IgE result. Nevertheless, a negative result in a test with a low cut-off is likely to rule out allergy as a trigger for symptoms and similarly a positive result for a test with a high cut-off is likely to confirm allergies are present. If you are using a self-test kit that measures the level of total IgE, check the leaflet provided with your test, or contact the manufacturer directly if you need further information on the cut-off for the particular test you are using as the cut-off can vary between manufacturers.

The SELFCHECK Allergy Test has greater than 97% agreement with laboratory based IgE tests, with a cut-off set at 150 kU/L to reduce the possibilities of a false positive result. Nevertheless, with tests with a relatively high cut-off, it is still possible to have allergies even if you have a negative result, and you should always speak with your pharmacist or doctor if you have any symptoms that concern you.

Further information on the SELFCHECK range of wellness self-testing kits can be found at selfcheckmedical.com