Allergy Tests Health Article

Definition

Allergy tests may be of two general types. In vivo tests that measure the immune response to an agent called an allergen that induces an allergic (atopic) reaction, and in vitro tests that measure the antibodies that mediate an allergic response. Such antibodies are those of the immunoglobulin E class (IgE) which have epsilon heavy chains which attach to mast cells.

Purpose

Allergy tests are performed to determine the cause of a person's allergic reaction. An allergic reaction is caused by the production of specific IgE antibodies against one or more antigens. Those antigens that elicit IgE production are termed allergens and are usually harmless substances. Some common allergens are described below.

• house dust mites and their waste
• hair, dander, and saliva of animals with fur or feathers
• cockroaches and their waste
• weed, grass, and tree pollens
• mold and mildew spores
• stinging insects such as bees, wasps, yellow jackets, hornets, and fire ants
• drugs such as penicillin, and sulfa drugs
• foods such as eggs, milk, nuts, and seafood
• ingredients found in dyes, cosmetics, and latex

Precautions

While allergy tests are safe for most people, there is always a possibility that the subject will experience a severe allergic reaction to an allergen used for in vivo testing. For this reason, the subject should be exposed to the lowest dose of allergen in the first phase of testing. In vitro blood tests are particularly appropriate for persons who have a history of severe allergy. In vitro testing may also be more appropriate for persons taking antihistamines, neuroleptics, or antidepressants, and for those with skin conditions all of which may interfere with skin test results.