Subtleties of Food Allergies
You might find interesting this article “Is Your Kid Truly Allergic? Tests Add to Food Confusion” in today’s Wall Street Journal. A few interesting observations from the article:
… A national sampling from 2005-2006, which also included blood tests, found that 9% of U.S. children had a sensitivity to peanuts, 7% to egg; 12% to milk and 5% to shrimp. But experts believe that only about one-tenth of those children will actually have allergic reactions to those foods. Even the true rate of fatal reactions to food allergies is hard to gauge: Estimates range from as low as five to as high as 200 per year.
… Blood tests measure the level of antibodies, called immunogloblin E (IgE), a body makes to a particular food. But having IgE antibodies doesn’t mean that a person will actually have an allergic symptom when they encounter it.
Skin-prick tests are slightly more predictive, but there, too, a red wheal in response to a skin prick doesn’t necessarily mean that a child will have an actual allergic reaction to that food.
… Allergy experts can make some guesses about the likelihood of a reaction based on test results, and they are starting to establish cutoff thresholds. In a skin-prick test, for example, a wheal smaller than 5 millimeters in diameter indicates a slim chance of a real allergy, says Dr. Sampson; a wheal greater than 10 millimeters is generally a good chance.
… researchers in Manchester, England, reported that when 79 children who tested positive for peanut IgE antibodies were given food challenges, 66 of them could eat peanuts safely.
… “Are these blood tests being overused? Possibly. Misinterpreted? Absolutely,” says Robert Wood, director of Pediatric Allergy and Immunology at Johns Hopkins Hospital.
… It’s estimated that 80% of children with allergies to milk, eggs, wheat, diary and soy outgrow them, usually by about age 5. But only about 20% of those with allergies to peanuts, tree nuts and shellfish do.