Allergy Testing
Category:
Allergy Testing
Known as: Allergy screen
Formal name: Allergen-specific IgE antibody test
Purpose:
Immunoglobulin E (IgE) is a protein associated 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, 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, they become sensitized. Their body perceives the potential allergen as a foreign substance and produces a specific IgE antibody that binds to mast cells (specialized cells in your tissues) and basophils (a type of white blood cell) in your blood stream. The mast cells are found in tissues throughout your body but are highest in concentration in your skin, respiratory system, and gastrointestinal tract. 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.
The allergen-specific IgE antibody test is used to screen for an allergy to a specific allergen. It measures the amount of that suspected IgE antibody in the blood. 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. Groupings of these tests, such as food panels or regional weed, grass, and mold panels, can be done. Alternatively, you and your doctor may pick and choose selectively from a long list of individual allergens suspected of causing your allergies.
The allergen-specific IgE test can be done using a variety of methods. The traditional method that has been used 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 assay that the testing lab is using.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
How is it used?
The allergen-specific IgE antibody test is done to screen for an allergy (a type I hypersensitivity) to a specific substance or substances when a patient presents with acute or chronic allergy-like symptoms.
The allergen-specific IgE antibody test may be done (instead of other medically supervised allergy testing) when the patient has significant dermatitis or eczema (also a sign of allergies), is taking necessary histamines or anti-depressants that would make other testing more difficult, or if a dangerous allergic reaction could be expected to follow another test.
The allergen-specific IgE antibody test may also be done to monitor immunotherapy or to see if a child has outgrown an allergy, although it can only be used in a general way; the level of IgE present does not correlate to the severity of an allergic reaction, and someone who has outgrown an allergy may have a positive IgE for many years afterward.