Allergy Blood Test: The Test Sample

What is being tested?
Immunoglobulin E (IgE) is a protein involved with allergic reactions; it is normally found in very small amounts in the blood. IgE is an antibody that functions as part of the body's immune system and helps to defend against "intruders". When someone with a predisposition to allergies is exposed to a potential allergen (such as food, grass or animal dander), they may become sensitized. Their body sees the potential allergen as a foreign substance and produces a specific IgE antibody that binds to mast cells which are specialized cells in your tissues and a type of white blood cell called basophils which are present in the blood. The mast cells are found in tissues throughout your body but have the highest in concentration in the skin, respiratory system, and gastrointestinal tract. At the time of the next exposure, these attached IgE antibodies recognize the allergen and cause the mast and basophil cells to release histamine and other chemicals which results in an allergic reaction that begins at the exposure site.

The allergen-specific IgE antibody test is used to check for an allergy to a specific allergen. It measures the amount of IgE antibody in the blood for the suspected allergen(s). Each selection is one separate test, and the tests are very specific: honeybee versus bumblebee, egg white versus egg yolk, giant ragweed versus western ragweed. Groups of tests, such as food panels or regional weed, grass, and mould panels, can be measured or you and your doctor can choose from a list of individual allergens which are suspected of causing your allergy.

The allergen-specific IgE test can be done using a variety of methods. The traditional method is the RAST (radioallergosorbent test) but it has been largely replaced in most laboratories with the newer IgE-specific immunoassay method. Some doctors refer to all IgE allergy tests as RAST even though this is a specific methodology and may not be the exact method that the testing lab is using.