Are We Overtreating Food Allergy?
The numbers of children with food allergy appears to have increased substantially over the last decade. Or has it? A study earlier this year called into question the necessity of food-restriction diets prescribed based on having positive skin or blood tests. This retrospective examination included 125 children between the ages of 1-9 years who had been placed on elimination diets based primarily on positive serum immunoglobulin E (IgE) immunoassay results. Almost all (96%) of these children had atopic dermatitis (AD), categorized as severe in almost half of the group, which was treated with elimination diet without attempting an oral food challenge (OFC). On OFC, 84%-93% of the foods being avoided were successfully returned to the diet, indicating that the vast majority of foods that had been restricted could, in fact, be tolerated despite positive testing. Thus, false-positive prick skin testing (PST) and IgE testing, with very literal interpretation of the results without verification objectively through food challenge, led to unnecessarily restrictive diets, parental anxiety, and the potential for nutrition deficiencies in children.
Other key points:
Children with a history of food anaphylaxis or a convincing history of a food reaction within the last 6-12 months were excluded. Most of the children with IgE testing above recommended 95% positive predictive value cut-off points were also excluded. However, 2 children with milk-specific IgE levels above this cutoff and a clinical history of tolerating small amounts of milk-containing foods were successfully challenged.
Many of the children had been placed on food restriction diets due to a positive immunoassay despite never having eaten the food previously or having tolerated it in the past.
All children who had a positive reaction to food during the OFCs experienced symptoms within 2 hours of ingestion.
There were no documented flares of AD on the day after an OFC was performed.
While children with larger PST wheals or higher food-specific IgE levels were more likely to experience a food reaction on OFC, the predictability was not clear and, even in children who did have positive OFCs, did not predict the severity of the reaction.
Children with an IgE level above the 95% predictive value for milk, egg, and peanut were more likely to experience symptoms on OFC but 2 children with those levels to milk were successfully challenged demonstrating that these thresholds are not infallible.
Why Is This a Game Changer?
This study would seem to confirm that use of PSTs and IgE testing should be confined to the realm of allergists. More importantly, positive tests are not necessarily automatically diagnostic of allergy. The clinical context for how these values were obtained should always be considered, and oral challenge is often necessary to provide such context. It is concerning to think how many children may be on food-elimination diets as a result of such nonspecific testing. The National Institute of Allergy and Infectious Disease released Guidelines for the Diagnosis and Management of Food Allergy in the United States late in 2010 and reiterated important distinctions between food sensitization and food allergy. In an earlier discussion on Medscape about the guidelines, Matthew Greenhawt, MD, MBA, Assistant Professor in the Department of Internal Medicine, Division of Allergy & Clinical Immunology at the University of Michigan Medical School noted that a positive PST and/or IgE results in patients in addition to a good supporting history strongly indicates a clinical allergy. However, similar results in children who are tested inappropriately and lack this strong history are very difficult to interpret. Many providers have placed too great an emphasis on positive results, considering them to be diagnostic of allergy in this situation. A good clinical rule of thumb should a primary care provider conduct any of these tests and prescribe elimination diets, would be for this recommendation to also be accompanied by a referral to an appropriate specialist who can adequately interpret all of the clinical and laboratory data and perhaps conduct a food challenge to determine whether such elimination diets are necessary. Furthermore, Dr. Greenhawt specifies caution in using 95% positive predictive values. These values were created within a very specific high-risk reference population, which may preclude generalization of these values to other populations, specifically if the prevalence of food allergy in those populations is different. As well, it remains very debatable if such cut-off values were intended for use in patients who had positive tests, but no history of developing symptoms to the particular food.
Medscape Pediatrics © 2011 WebMD, LLC
Cite this: Laurie E. Scudder. Game Changers in Pediatrics 2011 - Medscape - Nov 23, 2011.