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RAST Allergy Test

A RAST test (radioallergosorbent test) is used to test for allergies, including food allergies.

RAST tests are an effective way to determine what allergen may be triggering a person's allergy symtpom. They may also be performed to monitor the effectiveness of allergy shots, or desensitization treatment.

A negative result on a RAST test can help to rule out an allergy to a particular allergen.

A positive result on a RAST test suggests that you may have an allergy to a particular allergen. However, it may only mean that you are sensitized to the allergen and it may not be responsible for the symptoms. For this reason, it is important to compare the results of the RAST test with your medical history and physical exam.

If the results are incomplete, your doctor may order other allergy tests.

Advantages: The RAST test involves one needle stick, is quick to perform, and since the test evaluates blood drawn from the patient there is no risk of adverse reactions, such as anaphylaxis.

Disadvantages: The RAST test can be relatively expensive, results may take 1-2 weeks to obtain, and it may not be as accurate as other allergy tests, such as the food challenge test or intradermal skin test.

How does the RAST test work?

IgE antibodies are produced by the body and circulate in the blood to fight infections. They can also bind to allergens (substances to which you are allergic) and trigger an allergic reaction. If you are allergic to peanuts, dust mites or pollen, your IgE levels against those allergen will be elevated.

The RAST test is used to measure the levels of IgE antibodies against these specific antigens.

The lab will expose a sample of your blood to different test allergens. These may include animal dander (cat, dog, bird), grass pollens, tree pollens, dust mites or insects.

Allergens are usually tested in groups or "panels" of similar allergens. Your doctor will order specific panels based on your history, symptoms and suspected allergen.

How is the RAST test performed?

A blood sample is drawn from a vein in your arm. The blood sample is collected in a tube and sent to a lab for analysis.

What happens after getting RAST test results?

Depending on the results of your tests, your allergy symptoms and their severity, your doctor will recommend a treatment plan for your allergies. This may include the use of allergy medications, such as antihistamines, avoidance measure to prevent exposure to the allergen, allergy shots (immunotherapy) or other treatment options.

Where can I learn more about RAST testing?

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© 2010 Vivacare. Last updated November 11, 2010.

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Be sure to follow specific instructions given to you by your physician or health care professional.

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