Researchers examined records of more than 100 people with a known tree nut allergy to an individual nut. The findings? Despite showing a sensitivity to additional tree nuts during blood or skin prick tests, more than 50 percent of those tested had no reaction in an oral food challenge, in which an allergist fed the patient tiny amounts of the food in increasing doses over a period of time, followed by a few hours of observation to see if they have a reaction.
And get this: Almost none of the patients allergic to peanuts, which are legumes, were also allergic to tree nuts! "Too often, people are told they're allergic to tree nuts based on a blood or skin prick test," explained study author and allergist Christopher Couch, M.D. "They take the results at face value and stop eating all tree nuts when they might not actually be allergic."
And while 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, according to allergist and study co-author Matthew Greenhawt, M.D., a skin test or 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," he said. "The practice of avoiding all peanut and tree nuts because of a single-nut allergy may not be necessary. After an oral food challenge, people allergic to a single tree nut may be able to include other nuts in their diet.
Bottom line: If you've been avoiding all nuts based on a single known allergy, you should probably consider paying a visit to your allergist for an oral food challenge. Please, please don't ever attempt to stage an oral food challenge on your own. It should be supervised by a trained, board-certified allergist in a controlled medical setting in case a severe, life-threatening reaction occurs. To find an allergist near you, use the ACAAI allergist locator.