IgE Screening Doesn't Predict Food Allergy in Atopic Dermatitis Patients
By Anne Harding
NEW YORK (Reuters Health) - Serum immunoglobulin E (sIgE) levels are of limited use for predicting food allergy in children with mild to moderate atopic dermatitis (AD), according to new findings.
"The test is still a valid test, but not a valid test for screening," Dr. Jonathan Spergel of Children's Hospital of Philadelphia told Reuters Health in a telephone interview.
Checking sIgE is useful in children with AD and a history of a food reaction, he explained, but the positive predictive value of IgE levels is too low for the test to be used in screening patients with no history of food reactions.
Most patients who are sensitized to a food based on skin prick tests or sIgE measurements do not react to food challenges, Dr. Spergel and his team write in their report, published online November 23 in Pediatrics.
To better understand the usefulness of sIgE concentrations to predict clinical allergy, the researchers performed a prespecified analysis of the Study of the Atopic March (SAM), a multicenter dual-phase study of 1% pimecrolimus cream in 1,087 3- to 18-month-olds with AD funded by Novartis. SAM included a 36-month randomized controlled trial, followed by an open-label phase in which children received treatment up until six years of age, or until they had received 33 months of treatment.
By the end of the open-label phase of the study, 15.9% of the children had developed at least one food allergy, most commonly to peanut (6.6%), cow's milk (4.3%), or egg white (3.9%). Seafood, wheat, and soybean allergies occurred in 0.4%, 0.3%, and 0.4% of children, respectively. The more severe a child's AD at baseline, the more likely he or she was to develop food allergies.
Baseline sIgE values for cow's milk, peanut, egg white, and seafood was associated with an increased risk of developing allergies to these foods, while wheat and soybean sIgE levels were not. But patients' probability of developing a food allergy even at very high sIgE levels did not reach 0.90 for any food, and the probability was below 0.50 for most foods.
Negative predictive values were high for all decision points, ranging from 0.94 to 1.00.
Expert guidelines recommend against using sIgE levels to screen for food allergies, Dr. Spergel noted, but some pediatricians and family practitioners continue to do so. Because children with moderate to severe eczema were more likely to develop true food allergies, he added, physicians should consider referring children with moderate to severe eczema that can't be controlled for evaluation by an allergist or dermatologist.
The authors reported no conflicts of interest.