New Rules for Food Allergies (2)

Blood tests that measure immunoglobulin E (IgE) antibodies are very often misinterpreted, experts say. Having IgE antibodies to specific foods doesn't necessarily mean a person will have an allergic reaction when eating the foods. Skin-prick tests are more predictive, but they, too, measure IgE "sensitization," which may not result in an actual reaction. The report estimates that 50% to 90% of presumed allergies are not, in fact, allergies.

Still, many parents whose children have had a bad reaction to one food are anxious to know if they should avoid other foods, too, so they ask doctors to test many foods and avoid them to be safe. "

We get patients referred to us all the time who have been placed on very restrictive diets. They may be off 10 or 20 foods," says Dr. Sampson. "We go through a full evaluation and it turns out they are allergic to only one or two."

It's especially hard to pinpoint a true food allergy in young children with eczema, since they make IgE antibodies to many foods. "If you did 100 food tests, all 100 would be positive. That's what we see from patients coming in from around the country," says David Fleischer, an assistant professor of pediatrics at National Jewish Health in Denver, which specializes in allergy and respiratory diseases.

In a study published online in the Journal of Pediatrics this fall, a review of 125 children evaluated for food allergies and eczema at National Jewish in 2007 and 2008 found that over 90% of the foods they were avoiding were returned to their diets after food challenges.

The guidelines also recommend against using intradermal tests, in which a potential allergen is introduced deep under the skin, and skin-patch tests, a larger version of skin pricks, to diagnose food allergies. And they note that there is little scientific data to support a long list of other tests for allergy assessments, including hair analysis, facial thermography, which detects heat patterns and histamines in the skin, and immunoglobulin G tests, which purport to measure hypersensitivity to 100 or more foods at a time.

Melinda Beck at HealthJourna

Reference information: www.allergy.hk

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