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Study suggests tree nut allergies may be overdiagnosed

Patients diagnosed with an allergy to a single tree nut do not necessarily have to avoid all tree nuts, according to a new report.

By Amy Wallace
A new study found that people diagnosed as allergic to one type of tree nut do not necesarily have to avoid all tree nuts, researchers report. Photo by Pinkcandy/Shutterstock
A new study found that people diagnosed as allergic to one type of tree nut do not necesarily have to avoid all tree nuts, researchers report. Photo by Pinkcandy/Shutterstock

March 27 (UPI) -- New research by the American College of Allergy, Asthma and Immunology, or ACAAI, suggests that being diagnosed with one tree nut allergy does not necessarily mean a person needs to avoid all tree nuts.

The study found more than half of people diagnosed as allergic to one type of tree nut were able to pass oral food challenges to other tree nuts with no reaction -- meaning they are not allergic to that nut.

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Tree nuts include hazelnuts, walnuts, almonds, cashews and pistachios, but not peanuts, which are legumes.

"Too often, people are told they're allergic to tree nuts based on a blood or skin prick test," Dr. Christopher Couch, allergist and ACAAI member, said in a press release. "They take the results at face value and stop eating all tree nuts when they might not actually be allergic. We examined records of 109 people with a known tree nut allergy to an individual nut. They were tested for other tree nuts they had never eaten before using blood or skin prick tests. Despite showing a sensitivity to the additional tree nuts, more than 50 percent of those tested had no reaction in an oral food challenge."

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According to allergists, an oral food challenge, where a patient eats tiny amounts of the food in increasing doses over a period of time, is the most accurate way to diagnose food allergies. Oral food challenges should only be done under the care of an allergist in a medical setting with patients being observed a few hours after to make sure no allergic reaction occurs.

"Previous studies suggested people with a tree nut allergy, as well as those with a peanut allergy, were at risk of being allergic to multiple tree nuts," said Dr. Matthew Greenhawt, an allergist. "We found even a large-sized skin test or evaluated blood allergy test is not enough by itself to accurately diagnose a tree nut allergy if the person has never eaten that nut. Tree nut allergy should only be diagnosed if there is both a positive test and a history of developing symptoms after eating that tree nut."

Severe reactions to peanuts and tree nuts can cause anaphylaxis, a life-threatening allergic reaction that occurs when a person's immune system releases large amounts of histamines to combat an allergen, causing hives, swelling, trouble breathing, trouble swallowing, vomiting, drop in blood pressure and death. The treatment for anaphylaxis is an injection of epinephrine, often using a device such as an EpiPen.

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The study was published in the Annals of Allergy, Asthma and Immunology.

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