Diagnosing Food Allergies: Current Guidelines

Mother and child talking to doctor - Diagnosing Food Allergies: Current Guidelines


Health care professionals in the past used a wide range of criteria to diagnose and define food allergies, which made their prevalence difficult to estimate. Even today, many people mistake a food intolerance for a food allergy.

The definition of a food allergy is an "adverse health effect arising from a specific immune response which occurs reproducibly on exposure to a given food." Contact with a certain protein causes the body to produce an immunoglobulin E antibody, which can cause a wide range of symptoms that can vary in terms of their onset and severity. There is also a classification of food allergies that cause a delayed Non-IgE mediated response, such as in the case of celiac disease.

Currently more than 170 foods have been reported to cause IgE-mediated reactions, however eight foods are responsible for 90% of all food allergies. These eight foods include egg, milk, peanuts, tree nuts, wheat, fish, crustacean shellfish and soy.

Many people may self-diagnose a food allergy and severely restrict a child's or their own diet, putting them at risk for many nutritional deficiencies. In other cases, the allergy testing results may be misinterpreted due to a food-specific IgE being detected in the blood, causing people to avoid certain foods even though no allergic reaction has occurred.

The National Institute of Allergy and Infectious Diseases, of the National Institutes of Health, worked with numerous professional organizations, federal agencies and advocacy groups to organize an Expert Panel to review the literature and establish "best practice" clinical guidelines for the diagnosis and management of food allergies.

If a food allergy is suspected, the Expert Panel recommends an in-depth medical history and physical examination. Recommendations are made about the appropriate test to use to diagnosis a food allergy. For example, the Skin Prick Test may be used to assist in the identification of foods that may provoke a reaction but should not be used alone to diagnose a food allergy. The double-blind, placebo-controlled food challenge is considered the gold standard for diagnosing food allergies. However, these tests are expensive, time consuming and run the risk for inducing severe reactions in patients, so many physicians are hesitant to perform them. (Neither RDNs nor NDTRs should ever perform food challenges in isolation, due to the potential for severe reactions for which management is outside the scope of dietetics practice.)

The following list of procedures are non-standardized, unproven and are not recommended for the routine evaluation of the IgE-mediated food allergy:
  • Basophil histamine release/activation
  • Lymphocyte stimulation
  • Facial thermography
  • Gastric juice analysis
  • Endoscopic allergen provocation
  • Hair analysis
  • Applied kinesiology
  • Provocation neutralization
  • Allergen-specific IgG4
  • Cytotoxicity assays
  • Electrodermal test (Vega)
  • Mediator release assay (LEAP diet)

The Nutrition Care Process provides a framework for RDNs and NDTRs to provide evidence-based, standardized care to individuals with food allergies. Utilizing the NCP, the RDN should conduct a thorough nutrition assessment from which a nutrition diagnosis may be developed. Some examples of nutrition diagnoses related to food allergies include nutrient deficiencies, overly restrictive eating behavior and food- and nutrition-related knowledge deficit. The RDN will then create a detailed intervention addressing the individual's specific diagnosis and focusing primarily on education and follow-up.

Label reading is considered one of the important focus areas for RDNs when providing education to patients with food allergies. The NIAID Expert Panel report emphasizes the importance of addressing how to interpret ingredients on food labels. It states that if a food label contains precautionary labeling, such as "this product may contain trace amounts of allergen," the food should be avoided.

Patients may receive a list of foods to avoid, including ones that contain similar proteins as the allergen because of a "cross-reaction" that can occur, called the "oral allergy syndrome." The response and symptoms to this cross-reactivity can vary from person to person. The allergic reaction could be severe in the form of anaphylaxis or simply result in a temporary, itching or tingling sensation in the mouth, so there may or may not be a need exclude all of these foods from the diet.

The Expert Panel does not recommend restricting the maternal diet during pregnancy or lactation as a strategy for preventing the development of a food allergy. It recommends that all infants be exclusively breast-fed until 4 to 6 months of age, unless breastfeeding is contraindicated for medical reasons. In addition, there are specific recommendations for the use of soy infant formula, cow's milk and hydrolyzed formulas, and for the introduction of solid foods, which should not be delayed beyond 4 to 6 months of age.

RDNs can assist patients who have been diagnosed with food allergies by creating strategies for short-term and long-term avoidance of food allergens, while focusing on the nutritional adequacy of their overall diet. Specific focus areas in which RDNs may be most beneficial to patients with food allergies include safe and nutritious food substitution, label reading, advice for dining out in restaurants, and managing food allergens in schools.