Tree nut allergy: Avoiding all tree nuts 'may not be necessary'

More than half of patients who test positive for tree nut allergies based on blood or skin prick assessments experience no reaction to the nuts when consumed, a new study finds.

Lead study author Dr. Christopher Couch, a member of the American College of Allergy, Asthma, and Immunology (ACAAI), and colleagues suggest that oral food challenges should be the first port of call for the diagnosis of tree nut allergies.

The study results were recently published in the Annals of Allergy, Asthma, and Immunology.

According to the ACAAI, tree nuts - such as cashew nuts, Brazil nuts, hazelnuts, and walnuts - are among the eight most common food allergens in children and adults.

Symptoms of tree nut allergies may include abdominal pain, diarrhea, nausea, vomiting, itching of the mouth, throat, eyes, or skin, shortness of breath, and - in severe cases - anaphylaxis.

If an individual is allergic to one type of tree nut, then they are more likely to be allergic to other types. As a result, they are often told to avoid other types of tree nuts. The new study, however, suggests that such caution may not be needed.

Oral food challenge should be used to diagnose tree nut allergy

Dr. Couch and team came to their findings by analyzing the health records of 109 individuals with an allergy to an individual tree nut.

Using blood tests and skin prick tests, the researchers assessed the participants for allergies to other tree nuts that they had never consumed before. These tests showed that the participants had sensitivities to these nuts.

Next, the subjects underwent an oral food challenge, whereby they were required to eat small amounts of the tree nuts that they had shown sensitivities to in blood and skin prick tests. They were then closely monitored for any allergic reactions.

"Despite showing a sensitivity to the additional tree nuts, more than 50 percent of those tested had no reaction in an oral food challenge," says Dr. Couch.

Based on their findings, the researchers suggest that individuals with an allergy to a single tree nut should undergo an oral food challenge in order to confirm allergies to other tree nuts.

"We found even a large-sized skin test or elevated blood allergy test is not enough by itself to accurately diagnose a tree nut allergy if the person has never eaten that nut," says study co-author Dr. Matthew Greenhawt, chair of the ACAAI Food Allergy Committee. "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."

"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."

Dr. Matthew Greenhawt

The researchers note that an oral food challenge is the most accurate way to diagnose food allergies. However, they stress that such an assessment should only be carried out in the presence of a trained, board-certified allergist, in case of severe allergic reactions.

Learn why parents of children with food allergies assume that they are also allergic.