Q: My child tested highly positive to tree nut allergy, but I know she has eaten foods with almonds and hazelnuts without a problem. Does this mean, though, that she might go on to develop a nut allergy?
Dr. Sharma: It would first be important to confirm which specific tree nuts tested positive for your daughter. For many people, only some tree nuts test positive, while others test low or negative. Studies suggest about half of people with tree nut allergy are allergic to more than one nut. In children, the risk of being allergic to multiple tree nuts appears to increase with age.
There are also certain pairs of tree nuts that commonly “cross-react” because of similarity in their protein structures. These include pecan and walnut, cashew and pistachio, and almond and hazelnut. So someone who has had a reaction to cashew will likely also test positive and be allergic to pistachio, but may not be allergic to almond or hazelnuts.
Allergists therefore will interpret allergy test results in the context of the clinical picture – what happened when those nuts were eaten. If a child has a positive test result, but has been able to tolerate a type of nut without symptoms, then the result is likely a false positive.
For tree nuts that test low or negative but have never been eaten before, an allergist may consider supervised oral food challenges to determine whether those particular nuts trigger allergic reactions.
However, some allergists recommend avoidance of all tree nuts in patients with an allergy to any nut or nuts because of the risk of cross-contact among nuts during the manufacturing process.
Other allergists may suggest including some of the tolerated tree nuts in the diet depending on the child’s age, test or food challenge results, cross-reactivity of the nuts, and the child’s and a family’s preference.
If certain tree nuts are allowed in the diet of a child with other nut allergies, the allergist may advise only eating nuts that are hand-shelled, as a means of minimizing cross-contact risk during packaging. Be sure to discuss an individualized plan for your daughter with her allergist.
Dr. Sharma is an allergist, clinical researcher and assistant professor of pediatrics. He is Clinical Chief of the Division of Allergy and Immunology at Children’s National Health System in Washington, D.C. and Director of the Food Allergy Program. Questions submitted below will be considered for answer in the magazine.