Allergen-Specific IgE Antibody (RAST Test, Radioallergosorbent Test, Allergy Screen)

Test Description

The protein of the blood is composed of albumin and globulins. One type of globulin

is the group of gamma globulins, also called immunoglobulins or antibodies.

Gamma globulins are produced by certain white blood cells known as B lymphocytes

in response to stimulation by antigens. There are five types of immunoglobulins:

IgA, IgD, IgE, IgG, and IgM. IgE is the antibody of allergies.

Testing for allergies to various substances can be done via skin testing, however,

this can be uncomfortable for the patient and carries the risk of causing an allergic

reaction, since allergens are actually introduced into the body. Another way to test

for such allergies is the allergen-specific IgE antibody test. This test is also called

the radioallergosorbent test, or RAST test, because it involves the use of fluorescent

immunoassay to identify the specific allergens that are affecting the person. The

specific antigens, or allergens, are bound to a carrier substance. If the person is

allergic to a particular allergen, a specific IgE antibody in the person’s blood sample

will react with the allergen.

Normal Values

0 (No IgE detected)

1 (Equivocal/borderline)

Possible Meanings of Abnormal Values

Increased                                                                                                                                             

           Positive allergy to tested substance (Values vary from 2 through 6, with higher

           classifications indicating higher levels of IgE).

Contributing Factors to Abnormal Values

• Test results are affected by the type of allergen, length of exposure time to the allergen,

   and any previous hyposensitization therapy.

Interventions/Implications

     Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be

  drawn.

• No fasting is required before the test.

Procedure

• A 7-mL blood sample is drawn in a red-top collection tube.

• Gloves are worn throughout the procedure.

Post test

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued

  bleeding.

• Label the specimen and transport it to the laboratory.

• Report abnormal findings to the primary care provider

Clinical alert                                                                                                                             

Specific allergies found through this test should be noted in the patient’s medical

record.