Allergy Skin Tests
Two kinds of allergy skin tests are available, but only one is used in food allergy testing. This test, the percutaneous test, is commonly known as the scratch test or skin prick test. In this test, small amounts of purified allergens are placed on the skin, usually on the arm or back, and the skin is lightly scratched or pricked at these sites. A negative control (saline) and positive control (histamine) are used to compare results. The doctor looks for a wheal and flare response, consisting of a red, raised, possibly itchy bump at the scratch site. Patients rarely suffer a serious reaction to skin allergy testing.
The percutaneous test is highly specific to different antigens, but there is no standard for determining how much of a reaction constitutes a true allergic response. The other type of allergy skin test, the intradermal test, is more definitive but is not specific enough for food allergy testing. (Li 2002)
Photo information: A patient's back after an allergy scratch test. Some spots are visibly inflamed (wheal-and-flare response), indicating a positive result for those allergens. Photo by Skoch3, Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Skintest2.jpg). License: Creative Commons Attribution ShareAlike 3.0.