Food Allergy Testing: The Dangers of Improper Testing and Misdiagnosis

Recent research published in the journal Pediatrics indicates that many general pediatricians are ordering the wrong tests to try and diagnose food allergies. This is leading to over diagnosis of food allergies, unnecessary food avoidance and increased health care costs. Given that many patients are currently paying up to $650 for EpiPens, proper diagnosis of food allergy is critical not only for patient lifestyle, but also for controlling costs.

The study in Pediatrics revealed that primary care providers (PCPs) order an abundance of blood tests called “food panels.” A food panel looks for the presence of IgE (allergen antibody) to multiple different foods at once. Of the allergen panels ordered from a commercial laboratory in 2013, PCPs ordered 78.8% of the panel tests. Board-certified allergists, on the other hand, ordered the majority of single-food IgE blood tests with only 1.2% of their IgE orders being panel tests. PCPs who had been in practice for over 15 years were more likely to order food allergen panels than PCPs with less experience. Most concerning from the study was that compared to allergists, PCPs ordered more tests for unlikely causes of food allergies. In addition to putting patients through unnecessary testing, the PCPs also generated higher costs per patients compared to allergists.

Food allergies are diagnosed based on a combination of history suggestive of an allergic reaction and either positive skin or blood tests. Obtaining a thorough clinical history in a patient concerned about food allergy is critical because the history will influence the testing. In addition, the ability to correctly interpret the testing is essential. Skin prick testing is used in-office by board-certified allergists to look for the presence of specific IgE antibody to a specific food. Skin prick testing is very helpful because it is a very sensitive test, meaning that a negative test typically rules an allergy out. With a history of a reaction, a positive test will confirm a true IgE allergy. The skin test involves introduction of the allergen to the top layer of skin and measurement of any skin response. Interpretation of these tests should be done by a board-certified allergist who has gone through fellowship. An Allergy fellowship is an additional two years of training after pediatric or internal medicine residency including clinic time, hospital time, research and self-study all focused on allergy.

Blood testing for IgE to foods is readily available for any physician to order. However, not all physicians are trained in the correct interpretation of these blood tests. While the lab that performs the tests will provide the ordering physician with a normal “reference range,” the lab values require more in depth interpretation. There has been substantial research in the field of allergy to look at positive predictive lab values for the most commonly allergic foods. Board-certified allergists are familiar with this research and therefore better able to interpret the blood results.

As with skin testing for IgE, blood testing should only be performed for foods that are suspected allergies based on a thorough history. Some studies estimate that upwards of 30% of the general population will have a detectable level of IgE to a food with blood testing. However, only about 5% of patients have an actual food allergy. Therefore, physicians attempting to make a diagnosis of food allergy by blood testing alone will misdiagnose a majority of patients.

The improper ordering of food allergy panels by PCPs is leading to over diagnosis of food allergies. With that comes unnecessary dietary restrictions, potential nutritional deficiencies and higher healthcare costs. Also, recent studies have indicated delayed introduction of certain solid foods can increase the risk of developing food allergies. Thus, some children will develop food allergies due to avoidance that should have never been recommended to begin with.

As board-certified allergists, we are happy to see patients for discussion and testing of food allergies. We can perform skin testing in office with immediate results, but also recognize when blood testing for specific IgE to foods is indicated and which tests will be most helpful. The gold standard of food allergy diagnosis involves an oral challenge and board-certified allergists are comfortable with performing these challenges in clinic when necessary.

Stukus, DR et al. “Use of Food Allergy Panels by Pediatric Care Providers Compared with Allergists.” Pediatrics. November 2016.

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