Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

Allergy Blood Testing


At a Glance

Why Get Tested?

To help diagnose allergies; sometimes to monitor the effectiveness of immunotherapy (desensitization) treatment

When to Get Tested?

When you have symptoms such as hives, dermatitis, nasal congestion, red itchy eyes, asthma, or abdominal pain that your health care provider suspects may be caused by an allergy

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

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, and 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.

Each allergen-specific IgE antibody test performed is separate and 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, the health practitioner may pick and choose selectively from a long list of individual allergens suspected of causing a person's allergies.

While the traditional method for blood testing was the RAST (radioallergosorbent test), it has been largely replaced with newer IgE-specific immunoassay methods. Some health practitioners continue to refer to all IgE allergy blood tests as RAST even though it is not the exact assay that the testing laboratory uses.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test