Most tests for "allergy" are actually tests for allergic sensitization, or the presence of allergen-specific IgE. Most patients who experience symptoms upon exposure to an allergen have demonstrable allergen-specific IgE that specifically recognizes that allergen, making these tests essential tools in the diagnosis of allergic disorders.
The demonstration of sensitization is not sufficient to diagnose an allergy, however, because a sensitized individual may be entirely asymptomatic upon exposure to the allergen in question. Venom- and food-specific IgE has been reported in up to 25 and 60 percent of the general population, respectively [1-4]. Less commonly, patients who react to an allergen may not have any allergen-specific IgE that is detectable with routine testing [5,6]. Furthermore, IgE molecules recognizing specific epitopes of an allergen may differ in their ability to trigger allergic reactions, and the currently available tests do not distinguish among them.
The clinical response of a sensitized individual to the suspect allergen is best understood as a dynamic physiologic event with multiple variables, of which the presence of allergen-specific IgE is just one. Thus, allergy tests must be interpreted in the context of the patient's specific clinical history, and the diagnosis of an allergic disorder cannot be based solely on a laboratory result. This is true for in vitro assays, as well as for skin testing. (See "The biology of IgE".)
This topic provides an overview of in vitro tests for IgE-mediated allergic disease. Skin testing for allergic disease and the application of different tests to the diagnosis of food allergy are reviewed separately. (See "Overview of skin testing for allergic disease" and "Diagnostic evaluation of food allergy".)
Laboratory testing in cases of suspected anaphylaxis is reviewed in greater detail elsewhere. (See "Laboratory tests to support the clinical diagnosis of anaphylaxis".)