Many allergy specialists believe that food sensitivities are caused by a combination of factors, including poor nutrition, digestive problems, over-exposure to certain foods and a poorly functioning immune system. Allergy tests therefore need to be interpreted by a specialist, together with information about the individual’s diet and lifestyle.
A variety of tests exists to help allergy specialists identify suspect foods; these include skin prick testing, the IgE RAST, the IgG ELISA test and elimination diets. Tests of less certain accuracy and relevance to most people include sublingual drop testing, electrical testing, auricular cardiac reflex testing and applied kinesiology. The type of testing used varies in different countries and with different types of practitioner. An individual should therefore discuss appropriate allergy testing options with his doctor or allergy specialist.
Skin prick testing
The skin prick testing technique introduces tiny amounts of a potential allergen under the skin. This may be done by putting a small amount of the substance onto the skin and then pricking or scratching the area so that the allergen is introduced beneath the skin. The arms and back are common sites for testing, and several potential allergens may be tested at the same time. The area of skin is checked for a reaction after 15-20 minutes. Swollen or red skin on and around the test site is thought to show that the immune system has been activated and is interpreted as a positive result.
This type of test requires cautious interpretation as there is a wide margin for error, particularly when testing for food allergies. A food allergen that gives a positive result on the skin may not cause an allergic reaction when eaten. This test may therefore be considered as being more useful for revealing allergies to environmental substances (such as dust, mould, pollen and chemicals) rather than food allergies.
The RAST (Radio Allergo Sorbent Test) is carried out on serum separated from a blood sample and placed on samples of allergens. The RAST is the most accurate test for IgE-based allergies (including IgE-based food allergies), which usually produce an immediate reaction.
IgG ELISA test
The ELISA (Enzyme Linked Immuno Sorbent Assay) test, which uses blood serum to test reactions to various allergens, can test for IgG positivity. It can also show degrees of sensitivity. This method has proved to be highly accurate for IgG detection and can be used to pinpoint allergens causing more delayed allergic reactions.