IgE Levels Do Not Predict Food Allergy in Kids With Atopy

Diana Phillips

December 23, 2015

Serum immunoglobulin E (sIgE) levels are not clinically useful for predicting food allergy in infants with atopic dermatitis (AD), a study has shown.

The findings suggest that sIgE measurement is not a diagnostic substitute for food challenge in assessing food allergy development in this population, nor should sIgE levels alone justify food elimination diets in these children, Jonathan M. Spergel, MD, PhD, from the Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, and colleagues report in an article published in the December issue of Pediatrics.

AD and food allergy often occur together, leading investigators to question the link between allergic reactions to food and signs, symptoms, or clinical findings associated with atopy. For the current investigation, researchers used data from a dual-phase study designed to explore the long-term safety and efficacy of 1% pimecrolimus cream in infants with AD to examine the incidence of food allergy development. They also looked at the predictive value of food antigen–specific IgE measurements.

The study population included 1087 patients from 3 to 18 months of age with a diagnosis of mild to moderate AD for no more than 3 months before enrollment. All the patients were followed for the development of food allergy through a 36-month randomized double-blind phase and an open-label phase for up to 33 months. The children underwent ImmunoCAP measurement of sIgE for cow's milk, egg white, peanut, wheat, seafood mix, and soybean at baseline, at the end of the double-blind phase, and at the end of the open-label phase.

Approximately 16% of patients had developed a food allergy by the end of the study's open-label phase, most commonly to peanut (6.6%), cow's milk (4.3%), and egg white (3.9%). Allergies to seafood, wheat, and soybean were rare, developing, respectively, in 0.4%, 0.3%, and 0.4% of patients by the end of the open-label phase.

"The percentage of patients who developed 1 or more food allergies by the end of the study increased with increasing [Investigator's Global Assessment score] of AD severity at baseline," the authors report. Specifically, an Investigator's Global Assessment score of 2 or greater at baseline was predictive for development of food allergy.

The investigators assigned published and newly developed sIgE decision points for each of the six foods (of 5 kU/L for peanut, 5 kU/L for cow's milk, 2 kU/L for egg white, and 0.35 kU/L for seafood, wheat, and soybean) and tested their ability to predict definite food allergy.

Performance characteristics for sIgE decision points were determined using sIgE measured at baseline or at the end of the double-blind phase. "For the sIgE test to be clinically useful, it would need to have high predictive values," the authors explain.

The results show that negative predictive values for baseline sIgE were high for all decision points tested, and positive predictive values were low, the authors observe, noting that none of the positive predictive values exceeded 0.3.

At the end of the double-blind phase, using the same sIgE decision points, positive predictive values were increased relative to baseline, but values remained less than 0.6, Dr Spergel and colleagues report.

The high negative predictive values for the sIgE decision points used in this study suggest that "patients with mild AD with sIgE levels below these cutoffs would be unlikely to have or develop these specific allergies, and would not benefit from food challenges or elimination diets," they write.

"Similarly, elevated sIgE, as defined by the decision points tested, had very low [positive predictive values] for food allergy, both for sIgE values at baseline and at the end of the [double-blind] phase," the authors add.

"Thus, despite an increased likelihood of allergy development with increasing sIgE shown for cow's milk, egg, and peanut, our data do not support the use of sIgE testing for the diagnosis of food allergy in subjects without a history of reaction to that food."

Funding for this study was provided by Novartis Pharmaceutical Company. One coauthor has consulted for Valeant. The other authors have disclosed no relevant financial relationships.

Pediatrics. 2015;136:e1530-e1538. Abstract

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