Allergy tests for asthma can help get to the bottom of what's triggering asthma symptoms and help the doctor find the best asthma treatment. Up to 90% of children and 60% of adults with asthma have allergic triggers, and NIH guidelines recommend allergy testing for patients with persistent asthma. However, allergy tests may not be needed if the trigger history alone is very clear.
There are several types of allergy tests that might help with asthma, including skin, blood and other diagnostic lab tests to determine if allergic disease is present. Any allergy testing should be done based carefully on the allergy history.
Allergy skin tests are quick, fairly reliable, and cost-effective. Skin tests involve pricking the skin with or injecting specific allergens, such as dust or mold, under the skin. If there is an allergy to the allergen, special cells in the body react then release chemicals which trigger itching, swelling and redness. It is important to follow all of the instructions before the tests, such as stopping medications like antihistamines, which lowers the body's responses to allergens.
Allergy blood tests, including the radioallergosorbent test (RAST), are also used to detect the chemical reactions to specific triggers. They are less sensitive and cost more than skin tests and can give similar information. RAST may be needed for ultra-sensitive people where a skin test may pose a threat of a very severe allergic reaction, and patients do not need to stop taking their allergy medications before it. This test is also used in young children to rule out inhaled triggers.
After the testing is complete, the doctor must carefully review all of the information from the tests and the patient's history. The skin tests are likely better than RAST tests because they are more sensitive, and RAST tests alone should not be used to make an absolute diagnosis of allergy or make choices about environmental changes, such as removing or keeping a pet in the home.
Medications and avoiding triggers are the main ways persistent asthma is controlled. If asthma drugs are not enough to improve allergy and asthma symptoms, allergy shots may help. Allergy shots can reduce allergic symptoms common with cat dander, pollens, house dust mites and certain molds. Regular injections of allergens, given in increasing doses, make changes in the immune system that lower the chance of future allergic reactions.Testing to find what is triggering allergic asthma is valuable information that can make any treatment chosen by the doctor and patient work better.
Dr. Hennessey is an allergist with the Okemos Allergy Center, and an Associate Clinical Professor at the MSU College of Human Medicine in East Lansing.
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