Food allergies affect more than 1-2%—and less than 10%—of the population. The types of foods causing the most significant allergic reactions include peanuts, tree nuts, fish, shellfish, milk, eggs, wheat, soy, and seeds. To help identify those affected by this problem, three allergy associations in the United States recently released parameters for diagnosing and managing food allergies—defined as an “adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.” The document was prepared by the Joint Task Force on Practice Parameters, representing the American Academy of Allergy, Asthma & Immunology (AAAAI); the American College of Allergy, Asthma & Immunology (ACAAI); and the Joint Council of Allergy, Asthma & Immunology (JCAAI) and was published in the Journal of Allergy and Clinical Immunology.
For the purposes of the parameters, food allergy was not limited to IgE-mediated immunologic reactions “and is used to connote the induction of clinical signs and symptoms, as opposed to sensitivity, which indicates the presence of IgE antibodies to a food, often in the absence of clinical symptomatology,” the document states.
Among the ways to diagnose food allergies is serum sIgE testing, which uses fluorescence-labeled antibody assays to detect circulating IgE antibodies to foods for which allergies are suspected. Clinicians should be cautious about testing large panels or for multiple allergens because of the potential for false-positive test results. For peanuts, eggs, milk, fish, soy, and wheat, predetermined cutoffs should be used to assess whether food avoidance is necessary.
“Generally, higher sIgE levels are more likely to be associated with clinical reactivity, but the predictive value of sIgE levels varies across patient populations and might be related to the patient’s age, time since last ingestion of the suspected food allergen, and other underlying disorders,” the document states. Also, “sIgE testing can be useful in the clinical setting when there is a high degree of clinical suspicion but negative SPT [skin prick test] responses, and sIgE testing is particularly useful when SPTs are precluded by ongoing antihistamine therapy, moderate-to-severe skin disease, or dermatographism.”
Another option for testing is component-resolved diagnosis (CRD), which uses allergenic proteins derived either from rDNA or via purification from natural sources in order to identify a person’s sIgE reactivity to recombinant allergenic proteins. “But it is not routinely recommended even with peanut sensitivity because the clinical utility of component testing has not been fully elucidated,” according to the document, adding that more study is needed to assess the usefulness of CRD. In the meanwhile, “CRD is not routinely recommended for the diagnosis of food allergy, but CRD might be useful in certain clinical scenarios,” the authors wrote.
While weighing testing options, clinicians should also consider whether the patient has oral allergy syndrome (also known as pollen-food allergy), and they should order specific IgE testing to pollens in people who report limited oropharyngeal symptoms after eating foods that cross-react with pollen antigens.
The parameters warn against using unproven tests to diagnose food allergy, such as the allergen-specific IgG measurement, cytotoxicity assays, applied kinesiology, provocation neutralization, and hair analysis.