Do not use only blood tests to diagnose food allergy

The diagnosis of food allergy requires detailed history taking, followed by physical examination and appropriate testing to confirm the suspicion of food allergy. Patients with Atopic Dermatitis/Eczema produce very elevated levels of IgE and as a result, will produce a lot of “false positive” results in their blood tests. As a result, please see a qualified Allergy & Immunology specialist for proper evaluation and treatment.

Study warns of over-reliance on blood tests for food allergy

Last Updated: 2010-11-05 15:04:20 -0400 (Reuters Health)
By Megan Brooks
NEW YORK (Reuters Health) – In the absence of anaphylaxis, food-specific IgE tests aren’t sufficient evidence for cutting out food from a child’s diet, clinicians from Colorado warn in a report published online October 29 in The Journal of Pediatrics.
In a study of more than 100 children on food elimination diets based on positive serum IgE immunoassay results, oral food challenges (OFCs) demonstrated that most of the foods were being unnecessarily eliminated from the diet.
“The key message from our paper is that we need to be selective in ordering these serum blood tests for food allergy and be careful in interpreting the results before placing children on what may be unnecessary elimination diets, especially in children with atopic dermatitis,” first author Dr. David M. Fleischer from National Jewish Health in Denver, told Reuters Health in an e-mail.
“A referral to an allergist for possible supervised food challenges to truly determine whether or not there are food allergies may be necessary in some patients,” he added.
Dr. Fleischer’s team reviewed the charts of 125 children ages 1 to 19 years. Clinical history, prick skin test (PST), and serum allergen-specific IgE test results were obtained and all of the children underwent at least one OFC to determine IgE-mediated reactivity to a suspected food. The vast majority of the children (96%) had active atopic dermatitis at the time of evaluation.
The decision to perform OFCs was based on a combination of factors, the authors say, namely, a history of ever ingesting the food, the type of reaction, patient age, PST wheal size and food-specific immunoassay results.
OFCs were not performed on children with a history of a life-threatening reaction; a convincing history of a reaction within the previous 6 to 12 months; an immunoassay test result (level) that exceeded 95% predictive value for milk, egg, peanut, or fish; or an associated large PST.
According to the investigators, 89% of OFCs (325 of 364) performed with foods being actively avoided at baseline were negative. The foods included milk, egg, fruits, meats, shellfish, peanut, soy and wheat.
The authors point out that all reactions during the OFCs occurred within the two-hour observation period. There were no documented cases of atopic dermatitis flares on the day after an OFC.
“Depending on the reason for avoidance, 84% to 93% of the foods being avoided were returned to the diet after an OFC, indicating that the vast majority of foods that had been restricted could be tolerated at discharge,” Dr. Fleischer and colleagues report.
They further point out that many of the children were unnecessarily on “overly restrictive” diets that excluded foods that they had never eaten or foods that they once tolerated, based primarily on immunoassay test results.
“These tests are commercially available for any practitioner to order, but they should only be ordered if the clinical history is suggestive of a possible IgE-mediated reaction to a food,” Dr. Fleischer advises.
“The practice of ordering a large panel of serum IgE tests and eliminating a large number of foods without the expertise of a specialist such as an allergist to interpret these tests properly needs to change,” he added.
Compounding the problem, as the researchers note in their report, is that not enough allergy practices and centers perform OFCs, possibly due to cost or safety issues. In addition, managed care organizations may discourage referrals to specialists who can help interpret immunoassay test results.
“Unfortunately, we occasionally see children with failure to thrive due to severe dietary restriction based solely on in vitro immunoassay testing,” they note.

J Pediatrics 2010.



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