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More than 50% of patients with tree nut-allergy passed an oral food challenge
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Despite exhibiting skin or blood test sensitivity to peanuts and tree nuts, more than 50% of patients with a documented allergy to an individual nut passed oral food challenges consisting of additional nuts, according to data published in Annals of Allergy, Asthma and Immunology.
“Patients allergic to a particular tree nut often demonstrate co-sensitization to other tree nuts. In patients with peanut allergy, tree nut co-sensitization can occur in up to 86% of patients, although only 34% might display clinical reactivity — for example, symptom development after ingestion,” Christopher Couch, MD, from the division of allergy and clinical immunology at The University of Michigan School of Medicine and Allergy Asthma Clinic, and colleagues wrote. “Furthermore, many providers instruct children with peanut allergy to avoid tree nuts because of tree nut sensitization, despite no history of any tree nut reaction or low or absent sensitization.”
To assess the connection between oral food challenge (OFC) outcomes and tree nut sensitization, the researchers analyzed open tree nut OFCs performed at a referral center from 2007 to 2015. The results of the OFCs were compared with skin prick test (SPT) wheal size, food-specific immunoglobin E (sIgE), peanut co-allergy and tree nut sensitization only vs. tree nut allergy with sensitization to other tree nuts. A delayed OFC occurred more than 1 year after the time of an sIgE level below 2kUA/L.
The researchers recorded 156 tree nut OFCs performed in 109 patients, including 54 almond, 28 cashew, 27 walnut, 18 hazelnut, 14 pecan, 13 pistachio and two brazil nut. Eighty-six percent of the patients passed, with a 76% passing rate for those with a history of tree nut allergy. These individuals were challenged with a tree nut to which they were sensitized. Those who had tree nut sensitization only had a 91% passing rate.
“Too often, people are told they’re allergic to tree nuts based on a blood or skin prick test,” Couch 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. [In this study] despite showing a sensitivity to the additional tree nuts, more than 50% of those tested had no reaction in an oral food challenge.”
Individuals who had a tree nut sIgE less than 2 kUA/L had an 89% passing rate, and those who had sIgE levels of at least 2 kUA/L had a passing rate of 69%. Out of all challenges performed, 44 occurred in patients with peanut allergy and tree nut co-sensitization; 96% of these patients passed the tree nut OFC. When challenges were compared with SPCs, 61% of those who had a tree nut SPT wheal size of at least 3 mm passed. Those who failed had a larger mean wheal size (9 mm) compared with those who passed (4.8mm).
“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,” researcher Matthew Greenhawt, MD, chair of the ACAAI Food Allergy Committee, said in a press release “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. 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.” – by Katherine Bortz
Disclosure: Dr. Greenhawt is an expert panel member of the Guidelines for Peanut Allergy Prevention sponsored by the National Institute of Allergy and Infectious Diseases; has served as a consultant for the Canadian Transportation Agency and Aimmune Therapeutics; is a member of physician and medical advisory boards for Aimmune, Nutricia, Kaleo Pharmaceutical, Nestle, and Monsanto; is a member of the scientific advisory council for the National Peanut Board; has received honoraria for lectures from Thermo Fisher, ReachMD, and the Kentucky, Pennsylvania, Aspen, and New York allergy societies, the American College of Allergy, Asthma, and Immunology, the European Academy of Allergy and Clinical Immunology, and the UCLA-Harbor Medical Center; and is a member of the Joint Task Force on Allergy Practice Parameters. He has also received support from the National Center for Advancing Translational Sciences. C. Couch and T. Franxman report no relevant financial disclosures or conflicts of interest.
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Margaret Co, MD
This study supports the general caveat in this population of tree nut and peanut allergic patients that sensitization to a food (positive skin prick test or serum specific IgE) does not mean allergy or clinical reactivity. It demonstrated that in their population, most patients with a tree nut allergy and virtually all patients with peanut allergy were not allergic to other nuts to which they were sensitized.
The study raises the question of the wisdom of performing screening skin tests for tree nuts in peanut allergic individuals, as well as performing screening skin tests for tree nut allergy to which a patient has not reacted to, as this can lead to unnecessary tree nut avoidance. In my opinion, it still makes sense to do this for tree nut allergic but perhaps not in peanut allergic individuals. Very often, when a patient presents with a tree nut allergy, the identity of the tree nut is in question, and skin testing to all tree nuts frequently isolates the culprit nut. In this study, up to 24% of tree nut allergic patients did react to challenge with another tree nut: this is a population we would not want to miss.
In clinical practice, a referral to an allergist who will obtain a detailed history, perform skin testing, thoughtfully interpret these results, and finally if indicated, perform an oral challenge to other tree nuts will help determine which tree nut a patient can safely avoid.
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Melanie Makhija, MD
This study highlights something that allergists have always known, namely that testing isn’t perfect. When conducting skin tests and blood tests, we get a lot of false positives; however, as Couch et al have determined, if we conduct food challenges on patients sensitized to at least one tree nut, a portion of them may pass an oral food challenge to other tree nuts. Furthermore, among children sensitized to peanuts, even though there is cross-reactivity between tree nuts and peanuts, most of those children will pass a tree nut challenge.
For the pediatrician, this means that when parents are coming in with children who have experienced a reaction to peanuts, and the parents request a test for all allergies, it’s probably best to recommend them to an allergist. If an allergist tests them, then, even if they are positive, they can offer them a food challenge and can evaluate if the child is truly allergic or just sensitized, meaning they had a positive test.
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