Allergy Testing
Also known as: RAST test; allergy test
Formal name: Allergen-specific IgE antibody test
Related tests: Total IgE, Full blood count (FBC), White blood cell differential count , Eosinophil count, Basophil count
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.
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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
If you don't know what a word or a medical term means, try the
Mondofacto Online Medical Dictionary
.
