Allergy Testing

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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

At a Glance

Why Get Tested?

To test for suspected allergies.

When to Get Tested?

When you have symptoms such as hives, dermatitis, rhinitis (nasal blockage, sneezing), red itchy eyes, asthma, or severe reactions such as anaphylaxis that your doctor suspects may be caused by an allergy

Sample Required?

A blood sample taken from a vein in your arm

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.

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.

The Test

Common Questions

Ask a Laboratory Scientist

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.