Are tree nut allergies diagnosed too often?
27th March 2017 – An allergy to peanuts and tree nuts is the number one food allergy in adults and children in the UK.
Often, people who are allergic to a specific tree nut are told to avoid all other tree nuts but a US study suggests this may be unnecessary.
Tree nuts include almonds, cashews, walnuts, hazelnuts, Brazil nuts and macadamia nuts, but not peanuts which grow from the ground.
The new research is published in Annals of Allergy, Asthma and Immunology, the scientific publication of the American College of Allergy, Asthma and Immunology. It found that if you have a single tree nut allergy and have been advised to avoid other tree nuts based only on a positive blood or skin prick test, you may not be allergic to them after all. It may be worthwhile having an oral food challenge test under the supervision of a specialist to see if you may be able to include them in your diet.
For the study the records of 109 people allergic to one tree nut were examined. They were then tested for other tree nuts they had never eaten before using blood or skin prick tests. Despite these tests showing they had a sensitivity to the additional tree nuts, more than 50% of those tested had no reaction in an oral food challenge, which means they weren't allergic to that nut.
In an oral food challenge the person eats 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. It's considered the most accurate way to diagnose a food allergy but should only be undertaken in a specialist centre with experienced medical staff due to the possibility of a life-threatening reaction.
The study did not include oral food challenges to nuts a person had a documented history of having a reaction to when eaten.
The study noted that nearly none of the people allergic to peanut, but sensitised to tree nut, were clinically allergic to tree nut. This is the first study indicating that peanut allergic people may not need to avoid all nuts.
The research strongly suggests if you have an allergy to a single tree nut you should consider having an oral food challenge to diagnose any additional nut allergies, especially if you've never had a reaction to eating those tree nuts before.