AAAAI: Blood Tests for Food Allergy Found Inaccurate
source: Journal of Allergy and Clinical Immunology
Spears G, et al “Over-reliance on serum testing for IgE to food allergens results in inappropriate food elimination diets” J Allergy Clin Immunol 2009; 123: S179 source: Journal of Allergy and Clinical Immunology
Spears G, et al “Over-reliance on serum testing for IgE to food allergens results in inappropriate food elimination diets” J Allergy Clin Immunol 2009; 123: S179
WASHINGTON, March 16 — Common blood tests for food-specific serum immunoglobulins are often wrong about allergies and aren’t a good basis for restricting youngsters’ diets, researchers said here.
Results of supervised oral food challenges in 125 children failed to support most diagnoses of food allergies made on the basis of serum IgE testing, David Fleischer, M.D., of National Jewish Health in Denver, told the American Academy of Allergy, Asthma, and Immunology.
These challenges — in which children observed by professionals are fed increasing amounts of suspect foods over time to gauge their reactions — were performed on 63 foods being withheld from the children.
Dr. Fleischer and colleagues concluded that, in the absence of anaphylaxis, oral food challenges should be used to confirm food allergy status.
Unfortunately, physicians say, these tests are expensive, time consuming, and may require the facilities of a specialized center.
The Denver study included one boy who had 32 different foods removed from his diet, leaving him unable to eat any ordinary foods. He has passed all 25 food challenge tests performed so far, and is now eating relatively normal meals with his family, Dr Fleisher said.
Dr. Fleischer said the boy will undergo additional challenges on more foods. He said the child probably has some genuine food allergies and will require some dietary restrictions.
The investigators did not perform food challenges in children with diagnosed tree-nut allergies. Nor did they conduct challenges for other foods when the children had “convincing” previous evidence of reaction or extremely high food-specific serum IgE levels.
Consequently, few children with diagnoses of peanut allergies and none with soy allergies underwent food challenges. However, in five challenges that were performed on children with putative peanut allergy, all had negative results.
Food challenges were most likely to confirm serum IgE-based diagnoses of wheat allergy. Of six oral food challenges performed, three were positive and three were negative.
In most other cases, the oral-challenge produced negative results, and children were able to resume eating those foods.
Dr. Fleischer said the chief problem with moving toward the more accurate food challenge is the wide commercial availability of IgE-based food allergy diagnostic panels.
Melanie Gleason, P.A., of National Jewish Health, who also worked on the study, said parents and community physicians are often too quick to remove food from a child’s diet after a positive result from these tests.
Dr. Fleischer said serum IgE is only partially reflective of actual allergy, and that children often have high serum IgE levels across the board. That can lead to positive results for a given allergen even though the child can, in fact, tolerate the food.
As a result, food allergies should be confirmed with supervised food challenges, he said, particularly when children are being subjected to life-changing dietary restrictions.
Hugh Sampson, M.D., an allergist at Mount Sinai School of Medicine in New York, agreed that food challenges are needed to confirm initial diagnoses.
“Too many people are relying on a blood test or a skin test, which do not have a high level of specificity,” he said. “They [only] tell you what to suspect.”
However, Dr. Fleischer said medically supervised food challenges are beyond the capabilities of most community allergists or primary care physicians. He recommended that patients be referred to specialized centers, he said.
Dr. Sampson noted that there is a small amount of risk in such testing, and it can be expensive and time-consuming.
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POINT OF INTEREST
§ Explain to interested patients that blood tests for antibodies against specific food allergens are commonly used.
§ Explain that this study found that the results of these tests correlate poorly with results of supervised food challenges.
§ Note that this study was published as an abstract and presented orally at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
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