The Cleveland Clinic

Blood Testing for Allergies

Blood tests are sometimes performed to find out what triggers an allergic reaction and are often used if a patient has a skin condition or is taking medications, such as antihistamines. Such medications can interfere with an allergy skin test, which is a common test used to identify allergy triggers, but in general do not interfere with allergy blood tests.

The radioallergosorbent test (RAST) and the enzyme-linked immunosorbent assay (ELISA) test are two types of blood analyses that can be used to diagnose allergies. In both, a small amount of blood is taken from the allergy sufferer and analyzed for IgE antibodies (allergic antibodies) to specific antigens. High levels of these antibodies in the blood indicate an allergic reaction.

These blood tests may not be as effective as skin testing and tend to be more expensive, but can be useful in some situations.

Reviewed by the doctors at The Cleveland Clinic Department of Pulmonary, Allergy and Critical Care Medicine.

SOURCES: Asthma and Allergy Foundation of America. The Food and Drug Administration (FDA).

Reviewed by Walter M. Ryan, DO, on February 1, 2007.

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Last Editorial Review: 4/2/2007