According to the Asthma and Allergy Foundation of America, an estimated 50 million Americans now suffer from some type of allergies. Allergy symptoms may be mild or severe, acute or chronic, obvious or mysterious. Occasionally, allergy testing is necessary to help determine which substances may be causing a reaction and what the severity of that allergy may be.
Criteria for Testing
Not everyone with allergies needs to be tested. Indications for allergy testing include the presence of symptoms not responding appropriately to treatment; a previous severe reaction to food, medication or insect sting; or chronic asthma.
Types
Two basic types of allergy tests are used: skin testing and blood testing. Generally, skin testing is preferred because it is relatively quick and reliable. However, in some instances, skin testing is not possible if the person already has a severe rash. Also, blood testing can be done when a person is still taking an antihistamine to treat allergy symptoms, whereas in skin testing, the antihistamine needs to be stopped prior to the test.
RAST testing
The blood test for allergies is referred to as allergen specific IgE testing. Commonly called RAST testing, or RadioAllergoSorbent Testing, the test measures IgE antibodies, indicating allergy triggers. These antibodies are present because the body is trying to fight off something it sees as foreign or dangerous. With this test, it is possible to measure how much of each antibody is present.
Reliability
Analyses of IgE antibody levels to common food and airborne allergies are readily available, but it should be noted that testing for allergies with these methods may not always be helpful. A negative allergy blood test means no IgE antibodies to that substance were measured, but that does not completely exclude the possibility of a reaction. Also, it should be noted that the IgE levels measured by the test don't necessarily correlate with the severity of symptoms. Results of testing for food allergies with IgE levels are generally poor.
Acting on Results
All allergy test results need to be discussed with a physician so that a treatment and avoidance plan can be developed. In the case of severe allergies, emergency measures, such as carrying an epi-pen, should be discussed. Finally, in the case of certain food allergies in children, testing may be repeated in the future to help determine whether or not a particular allergy has resolved itself.
References
- Asthma and Allergy Foundation of America: Information about asthma and allergies
- "Allergy Testing"; American Family Physician; August 15, 2002
- Allergy Blood Testing: Common Questions
