Lab Tests for Food Allergies Not Diagnostic by Themselves, say NIAID Guidelines

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March 11, 2011

Laboratory tests that detect elevated levels of allergen-specific IgE antibodies can be used to identify offending foods but should not be the sole basis of diagnosis, according to recent guidelines from an expert committee.

Published in the December issue of the Journal of Allergy and Clinical Immunology, the new guidelines are intended to standardize the diagnosis and management of food allergies. The National Institute of Allergy and Infectious Diseases (NIAID) funded and organized the project that produced the guidelines.

The Centers for Disease Control and Prevention (CDC) estimates that 4% of children younger than 18 and 2% of adults have food allergies. Such allergies are sometimes life-threatening and have no cure but can be managed by avoiding foods that trigger reactions and by treating symptoms. A wide range of foods can cause allergic reactions, which produce symptoms that include hives, tingling or swelling in the mouth, rash, difficulty breathing, abdominal cramps, vomiting, and diarrhea.

To compile the guidelines, NIAID worked with 34 professional organizations, advocacy groups, and federal agencies to convene a panel of 25 experts. The expert panel systematically reviewed more than 400 studies before drafting the guidelines, which include 43 recommendations.

Many of the recommendations address diagnosis because food intolerances are often confused with food allergies. True allergies involve a cascade of immune system responses while food intolerance can produce some of the same symptoms but does not involve the immune system. People with food intolerance can usually eat small amounts of the food without a reaction. In contrast, allergic reactions can result from eating even the tiniest amount of the offending food.

Doctors sometimes order blood tests to help diagnose food allergies and, based on positive results, counsel patients to avoid those foods. However, a proper workup requires a detailed medical history, a thorough exam, some laboratory tests, and oral food challenges for confirmation, according to the guidelines. These steps are all necessary because multiple studies show that 50% to 90% of people who suspect they have a food allergy don't actually have one.

The guidelines recommend skin and blood tests for food allergy evaluation. These include skin prick tests and allergen-specific immuglobulin E (IgE) tests. The guidelines also advise against using nonstandardized and unproven assays, such as the allergen-specific IgG4 test some doctors now use.

Doctors should give oral food challenges to properly diagnose food allergies. If the challenge produces no symptoms, the doctor can rule out a food allergy. If the medical history and lab tests indicate an allergy, and the food challenge elicits symptoms, then a food allergy diagnosis is supported, the guidelines say.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Boyce et al. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report. Journal of Allergy and Clinical Immunology. Available online at http://www.jacionline.org/article/S0091-6749(10)01569-1/fulltext through http://www.jacionline.org. Issued December 2010. Accessed February 15, 2011.

Todd Neal. Comprehensive Food Allergy Guidelines Released. MedPage Today. Available online at http://www.medpagetoday.com/AllergyImmunology/Allergy/23742 through http://www.medpagetoday.com. Published December 6, 2010. Accessed February 15, 2011.

James T. Li, MD. Food Allergy vs. Food Intolerance: What's the Difference? Mayo Clinic. Available online at http://www.mayoclinic.com/health/food-allergy/AN01109 through http://www.mayoclinic.com. Posted June 5, 2009. Accessed February 15, 2010.

(October 3, 2008) Centers for Disease Control and Prevention. Food Allergies. Available at http://www.cdc.gov/healthyyouth/foodallergies/ through http://www.cdc.gov. Accessed February 2011.