CAUSES
β’ Any food or ingested substance can cause allergic reactions. Most commonly implicated foods include cowβs milk, egg whites, wheat, soy, peanut, fish, tree nuts (walnut and pecan), shellfish, melons, sesame seeds, sunflower seeds.
β’ Several food dyes and additives can elicit allergic-like reactions
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DIFFERENTIAL DIAGNOSIS
β’ A careful history is necessary to document a temporal relationship with the manifestations of suspected food hypersensitivity
β’ The gastrointestinal, dermatologic, respiratory, neurologic or other systemic manifestations may mimic a variety of clinical entities
β’ Eosinophilia in either blood or tissue suggests atopy
β’ 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. Skin testing using the suspect food may be helpful. An oral challenge may 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).
β’ Radioallergosorbent (RAST) test can also detect specific IgE antibodies to offending foods. In certain laboratories, the RAST test was almost as accurate as a skin test in predicting positive oral challenges.
β’ 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.
β’ The provocative injection and sublingual provocative tests are both highly controversial and have been proven to be useless for the diagnosis of food allergy
β’ The leukocytotoxic assay is an unproven diagnostic procedure and is not useful for the diagnosis of allergy
SPECIAL TESTS : Stool exam, mucus, eosinophilia
IMAGING Upper GI series for gastric antral infl ammation, in rare cases
DIAGNOSTIC PROCEDURES :
. Elimination and challenge test
. The best procedure for confi rming food allergy
. First, the suspected food is eliminated from the diet for 1-2 weeks
. The patientΒfs symptoms are monitored. If the patients symptoms disappear or substantially improve, an oral challenge with the suspected food should be
performed under medical supervision.
. Optimally, this challenge should be performed in a double-blind, placebo controlled manner
. Patients with a history of anaphylaxis should not generally have an oral challenge
. 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