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Tuesday, July 21, 2009

Food Allergy Tests Can Be Unreliable

There are two major types of food allergy tests. A blood test checks to see whether or not you have a particular antibody called IgE. Skin prick tests reveal reactions to the potential allergen.

Both are good in certain ways. Both also have major problems that people must understand.

Emily Sohn gave some basics in the Los Angeles Times.

IgE tests are very good at confirming the lack of an allergy -- but only when the antibody is just plain missing. In many cases, for reasons scientists don't understand, just about everybody has antibodies to foods they don't react to. ...

These skin tests are fairly reliable when they're negative. Positive reactions to foods, on the other hand, are wrong up to 50% of the time.

Someone with a milk allergy might develop bumps from beef and pork pricks, and someone with an egg allergy might react to chicken and turkey pricks, simply because the proteins in those food groups are similar enough, or because a person has sensitive skin.

Allergy tests also have the same underlying problem that plagues testing for lactose intolerance. Even when the test predicts the allergy properly, it can't predict the severity of the reaction.

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