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How to Know If You Have a Food Allergy

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Nearly every school nowadays has peanut-free lunch options for kids with peanut allergies, and it has become de rigueur at children's get-togethers and birthday parties to include alternatives for kids with dairy allergies. All this anecdotal evidence suggests that food allergies are skyrocketing. There's scientific evidence as well. A recent study in the Journal of Allergy and Clinical Immunology found that peanut allergies alone have tripled over the past decade.

But another study just published in the heavyweight Journal of the American Medical Association suggests something else may be going on. Namely, that many of these food allergies may be a result of simple confusion—confusion over what defines a food allergy, how we test for them, and how we treat them. "The world of food allergies is evolving all the time," says the study's lead author Jennifer Schneider, MD, MS, healthy policy fellow at Stanford University and the VA Palo Alto Healthcare System. "There's not a widely accepted clinical test for diagnosis," she says, "And as practitioners we haven't been able to definitively say what a food allergy is."

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THE DETAILS: The study reviewed existing literature on the prevalence, diagnosis, management, and prevention of food allergies. The authors analyzed 72 studies of food allergies to cow's milk, eggs, peanuts, tree nuts, fish, and shellfish, and came up with some interesting findings.

Most important, there doesn't seem to be a single accepted mode of diagnosing food allergies. Some of the studies under review used self-reports (the authors noted that allergy prevalence was always higher when this method was used), others used skin-prick tests, and still others used a blood test that measures immunoglobulin E (IgE), an antibody produced during an allergic reaction. Very few studies used food challenges, a clinical test whereby a patient is exposed to the suspected food and monitored for allergic reactions. This despite the fact that food challenges are by far the most accurate tests for diagnosing food allergies. Due to this lack of diagnostic uniformity, the authors noted that it's unclear whether food allergy prevalence actually is increasing. Some studies suggested that 1 to 2 percent of the population suffers from them, while others put the number as high as 10 percent.

WHAT IT MEANS: Bottom line is, the study authors believe the lack of uniformity in diagnosing and defining food allergies is likely leading to an overdiagnosis of the condition. Other research has shown that people with purported food allergy symptoms (such as rashes or stomach aches) who test positive for food allergies via skin prick or IgE blood test have a less than 50 percent chance of having a food allergy. Which could lead to unnecessary dietary restrictions that result in nutrient deficiencies. It can also cause angst, and needlessly put people in awkward social situations.

Furthermore, "People in the general population often dismiss food allergies because they don't distinguish between food intolerance and food allergies," says Dr. Schneider. A food allergy is a serious medical condition, she says. It involves a serious immune system reaction, whereas a food intolerance does not.

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So if doctors can't agree on definitions and diagnoses, where does that leave the rest of us? Here are a few signs and tests you may want to discuss with your doctor before eliminating foods you think you're allergic to:

Know the difference between allergies and intolerance.
"Food intolerances don't cause life-threatening symptoms," says Jacqueline Pongracic, MD, division head of Allergy & Immunology at Children's Memorial Hospital in Chicago. "And, with food intolerance, typically the degree of symptoms is related to the amount of food you consume." For instance, a small amount of ice cream may not give you a stomachache if you're lactose intolerant, but if you have a true milk allergy, that tiny amount could trigger instant wheezing, hives, or even more severe reactions.

Also, food intolerances don't always occur every time you're exposed to a food. "With a food allergy, it's very consistent," she says. "Each time you're exposed, you get the reaction." If you suspect you or a child might have a food allergy, Dr. Pongracic suggests monitoring the reactions to see whether they occur every time the food is consumed before you actually visit a doctor. "There are so many situations where someone consumes multiple foods at the same time, which make it tricky to determine what the culprit is," she says. "Of course, if the reaction is severe, I recommend you get an evaluation to see what caused it."

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Consider a food challenge.
Dr. Pongracic agrees with the study findings that doctors need to come up with some uniformity in defining and diagnosing food allergies. And as with the study authors, she believes food challenges are the gold standard for diagnosis. "A food challenge mimics how someone consumes a food, and it's helpful especially in situations where it's not entirely clear that the person has an allergy or an intolerance," she says.

In a food challenge, Dr. Pongracic says, an allergist will ask a parent or patient to prepare a potentially allergenic food at home and bring it into a clinic. Once there, a doctor or nurse will gradually feed it to the patient while monitoring symptoms and taking care to have emergency medication on hand in case of a reaction. The test can take half a day, she says, and the method isn't always popular with doctors, as it's time consuming, labor-intensive, expensive, and occasionally risky. But it can be worth it if you really need to know what you're dealing with.

Don't discount the other allergy tests.
Though food challenges are the gold standard, "we can't rely on just one diagnostic method," says Dr. Pongracic. "A lot of these false-positive diagnoses happen when someone is basing a diagnosis on only one test." The first time you visit an allergist for a potential food allergy, he or she will probably do a skin prick or the IgE blood test, she says. But it's what happens next that's important. Negative test results, she says, are very reliable. But if the test is positive, Dr. Pongracic recommends that you ask your doctor to confirm the result with a food challenge. If he or she says no, and doesn't give you a good reason why, it might be good to get a second opinion.

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