Food allergy is a hypersensitivity reaction which is caused by certain foods. Adverse reactions after food ingestion may be caused by immunologic mechanisms, such as the classic IgE allergic response, or by non-immunologic mediated mechanisms.
Any food or ingested substance can cause an allergic reaction. The most commonly implicated foods include cow's milk, egg whites, wheat, soy, peanut, fish, tree nuts (walnut and pecan), shellfish, melons, sesame seeds, sunflower seeds, and chocolate. Several food dyes and additives can elicit allergiclike reactions.
Persons with allergic or atopic predisposition are at increased risk of hypersensitivity reaction to foods. Increased risk is also associated when other family members have a history of food hypersensitivity.
Eosinophilia in either blood or tissue suggests atopy.
Epicutaneous (prick or puncture) allergy skin tests are useful in documenting IgE mediated immunologic hypersensitivity. In most clinical situations, the allergy skin tests are good for screening. An oral challenge should be completed to accurately determine the clinical hypersensitivity. The overall agreement between allergy skin testing and oral food challenge is approximately 60% (i.e., a positive skin test showing a positive challenge reaction to a particular food).
Radioallergosorbent (RAST) test can also detect specific IgE antibodies to offending foods. In certainlaboratories, the RAST test was almost as accurate as a skin test in predicting positive oral challenges.
Leukocyte histamine release and assays for circulating immune complexes are predominantly research procedures and are of limited use in clinical practices. Assays for IgG and IgG 4 subclass antibodies are commercially available. There are no convincing data that these tests are reliable for the diagnosis of food allergy.
The elimination and challenge test is the best procedure for confirming food allergy. First, the suspected food is eliminated from the diet for 1-2 weeks. The patient's symptoms are monitored. If the patient's symptoms disappear or substantially improve, an oral challenge with the suspected food should be performed under medical supervision. Most allergic reactions will occur within 30 minutes to 2 hours after the challenge, although late reactions have also been described, which may occur from 12-24 hours
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