Most parents, and many physicians, do not understand the limitations of food allergy testing. As I am sure is common among physicians, I frequently receive requests for food allergy testing; parents do not realize that the strategy for food allergy testing is not straight-forward and has not advanced significantly for decades. This information is detailed in a recent study and associated editorial (J Pediatr 2015; 166: 97-100, editorial 8-10: “Pitfalls in Food Allergy”).
The study was a retrospective review of all new patients seen at a pediatric food allergy center (2011-2012). This involved a review of 797 new patients.
- Of 284 patients who had received a food allergy panel, only 90 (32.8%) had a history warranting evaluation for food allergy.
- Among 126 individuals who had food restrictions imposed based on food allergy panel testing, 112 (88.9%) were able to re-introduce at least 1 food into their diet.
- The positive predictive value of food allergy testing was 2.2%.
So what can we learn from this study and editorial?
Misdiagnosis often relates to a lack of understanding regarding serum IgE-based testing. First of all, many children with atopic dermatitis (and other atopic conditions) have elevated total IgE which results in more false positives. In addition, a positive IgE test for a specific food indicates sensitization but not necessarily an allergy.
Strategy for testing (recommended by editorial):
- “The key to the diagnosis of food allergy cannot be overstated; it begins with a detailed clinical history”
- Testing should be “limited in general to the food(s) in question.”
- When there is uncertainty, oral food challenges can be performed by specialists.
- “If a patient is consuming a food without clinical symptoms of allergy, allergy testing should not be done to that food.”
Bottomline (from authors’ conclusion): “Food allergy panel testing often results in misdiagnosis of food allergy, overly restrictive dietary avoidance, and an unnecessary economic burden on the health system.”
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