Immunoglobulin E (IgE) is a class of antibody (immune protein) associated with allergic reactions. It is normally found in very small amounts in the blood. This test measures the amount of allergen-specific IgE in the blood in order to detect an allergy to a particular substance.
IgE is an antibody that functions as part of the body's immune system, its defense against "intruders." When someone with a predisposition to allergies is exposed to a potential allergen such as food, grass, or animal dander for the first time, that person becomes sensitized.
The person's body perceives the potential allergen as a foreign substance and produces a specific IgE antibody that binds to specialized mast cells in the skin, respiratory system, and gastrointestinal tract, as well as to basophils (a type of white blood cell) in the bloodstream.
With the next exposure, these attached IgE antibodies recognize the allergen and cause the mast and basophil cells to release histamine and other chemicals, resulting in an allergic reaction that begins at the exposure site.
A total IgE test measures the overall number of IgE antibodies in the blood, while a specific IgE test measures for a response to individual allergens.
Each allergen-specific IgE antibody test performed is separate and very specific; for example, it will test honeybee versus bumblebee, egg white versus egg yolk, and giant ragweed versus western ragweed.
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