Table of Contents
Allergy Testing Definition and Information
Allergy Testing is a diagnostic procedures to determine the allergens responsible for hypersensitivity reaction. The most specific allergy test is the allergy skin test, also called a scratch test or a patch test. For this test, the allergist uses the inside of the arm or a section of the back to expose the body to suspected allergens. The allergist places a small drop of a solution containing the allergen on a marked spot on the skin, then uses a sterile picklike instrument to scratch the surface of the skin.
This exposes the immune system to the suspected allergen. If a wheal (raised welt) forms on the site within 15 minutes, the test is positive for the allergen. For a typical allergy skin test, the allergist may test a number of substances at the same time, each on a different site on the skin. The allergy skin test tells the allergist the precise allergies an individual has. The allergy skin test helps the allergist strategize the most effective treatments and is necessary before desensitization treatments.
Though it is rare, a person who has a strong allergy may have an intense reaction during an allergy skin test, including anaphylaxis, that requires urgent medical treatment.
A radioallergosorbent test (RAST) is a blood test that measures the amount of immunoglobulin E (IgE) in the blood circulation when allergy symptoms are present. An amount higher than normal level of serum IgE indicates a hypersensitivity reaction. The RAST does not identify the specific allergen. There is no risk for the RAST to cause a hypersensitivity reaction because it does not expose the person to any allergens.
A food-elimination diet is the preferred allergy test to identify potential food allergies. The person eliminates specific foods from his or her diet for several weeks, then reintroduces them one at a time and notes whether there are corresponding symptoms. An important part of a food-elimination diet is keeping an accurate food diary that records symptoms and other perceptions during the test. This allergy test is somewhat subjective, though often results in connecting specific foods with allergy symptoms.
Another test for food allergies is the food challenge, which takes place in a hospital. The allergist gives the person certain foods, often mixed with other foods, without the person knowing, then observes and documents any symptoms that develop. There is a risk that the food challenge may cause a hypersensitivity reaction that would require immediate medical intervention; this is why the test takes place in a hospital or other emergency-ready facility.
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