Food allergy blood tests overdiagnose allergy

A study at National Jewish Health set out to evaluate whether children living on restricted diets based on tests using immunoassay tests were unnecessarily avoiding certain foods.
Immunoassays detect antibodies in the blood to specific foods, which can potentially cause allergic reactions. Interpretation of the results, however, can be tricky. The tests' ability to predict true food allergy has been validated for only five foods - cow's milk, hen egg, fish, peanut and tree nuts.

For all other foods, the results are suggestive but not definitive. Low test values suggest that a child's immune system is sensitised to the food, but not necessarily to the extent that it will cause an allergic reaction. Higher values suggest an increasingly likelihood of true food allergy. But none of the tests is 100% accurate in predicting clinical food allergy.

Many factors, including patient and family history, physical examination, and blood and skin tests, need to be assessed when diagnosing food allergies while the oral food challenge, in which patients consume the suspected allergenic food, remains the gold standard test.

The National Jewish Health researchers conducted a retrospective chart review of 125 children evaluated for suspected food allergies. The physicians re-assessed blood tests, patient history, including any previous reactions to food, the type of reaction, the patient's age, and the result of skin testing for food allergy.

Children in the study were avoiding 177 different foods based primarily on previous blood test results. In many cases, especially those with high test results for egg, milk, shellfish, peanut and tree nut, National Jewish Health elected not to perform oral food challenges. They did perform oral food challenges for 71 foods or about 40% of the cases where the clinical allergy was equivocal and it was important to determine whether or not the patient had food allergy. In 86% of those cases, the child passed the food challenge and the food was restored to the child's diet. Overall, 66 of the 177 foods avoided because of blood tests were restored to children's diets. For the entire study, 325 foods were restored to the diets of 125 children.

The problem can be especially acute among patients with eczema as research suggests that specific foods can cause flare-ups in about one third of eczema patients. They commonly have high immunoassay tests to a variety of foods, many of which are not truly allergenic. As a result, many mistakenly avoid foods they believe are causing flare-ups, but neglect basic skin care that is vital to improving the eczema. One hundred and twenty of the 125 children in the study had eczema.

Being able to restore such a large number of foods to a child’s diet obviously makes both ensuring that the child is being properly nourished and catering for the family very much easier.

David M. Fleischer, S. Allan Bock, Gayle C. Spears, Carla G. Wilson, Naomi K. Miyazawa, Melanie C. Gleason, Elizabeth A. Gyorkos, James R. Murphy, Dan Atkins, Donald Y.M. Leung. Oral Food Challenges in Children with a Diagnosis of Food Allergy. The Journal of Pediatrics 2010

First Published in October 2010

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