What Is The Best Test For Diagnosing Food Allergies?

The most important component in diagnosing allergy to a food is the patient’s history. A food allergy is most often suspected when a particular item was eaten prior to the onset of acute symptoms. In some cases, the implicated food was eaten by itself, making it easy to identify the probable source of symptoms. In many cases, however, several foods were eaten as part of the same meal, making it more difficult to sort out which food the patient reacted to. When food-induced symptoms occur frequently without an obvious consistent trigger, a daily diary may be very helpful.

The patient records the timing of meals, amount of food eaten, how the food was prepared, all activities (such as exercise) that were performed in relationship to the reaction, and the symptoms and duration of the reaction. Following the initial history and possibly the extended use of a diary, allergy testing should be performed to confirm which food caused the reaction. Generally, testing can be limited to those foods that were eaten 2 or fewer hours prior to the onset of symptoms. In cases of mild food reactions, allergists perform prick/puncture skin testing. If the prick/puncture test is negative to a food, the person is considered to have no allergy to that food. Intradermal skin testing to foods should never be performed, either as an initial test or as a secondary test in patients who have negative prick/puncture tests.

When used as an initial test, the large amount of allergen injected with this type of test can induce a dangerous systemic reaction. When used as a secondary test,intradermal tests yield very nonspecific results such that a positive result is just as likely to occur in a patient who has no allergy as it is in a patient who has a proven allergy. In patients with histories of more severe reactions to foods, the physician may advise that you undergo blood allergy testing for safety reasons. The most reliable blood test for diagnosing food allergies is the ImmunoCap assay which determines the amount of IgE directed at specific foods. Although this blood test for food allergies is not quite as sensitive as prick/puncture skin testing, it is still an extremely accurate test, which yields valid results. Tests that determine the presence of IgG to foods have not proven useful in diagnosing food allergy.