Unreliable blood tests cause overdiagnosis of food allergy in the US

More than 11 million Americans, including three million children, are estimated to have food allergies, most commonly to milk, eggs, peanuts and soy. The prevalence among children has risen 18% in the past decade, according to the Centers for Disease Control and Prevention. While the increase appears to be real, so does the increase in misdiagnosis.

The culprit appears to be the widespread use of simple blood tests for antibodies that could signal a reaction to food. The tests have emerged as a quick, convenient alternative to uncomfortable skin testing and time-consuming ‘food challenge’ tests.

But while the blood tests can help doctors identify potentially risky foods, they aren’t always reliable. A 2007 issue of The Annals of Asthma, Allergy & Immunology reported on research at Johns Hopkins Children’s Center, finding that blood allergy tests could both under- and overestimate the body’s immune response. A 2003 report in Pediatrics said a positive result on a blood allergy test correlated with a real-world food allergy in fewer than half the cases.

Children can have their diet restricted unnecessarily. Avoiding certain foods because an allergy is suspected may actually make children more sensitive to those foods when they finally do eat them.

The only true test of a food allergy remains whether you can eat a food and not react to it.

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First published in April 2009

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