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A difficult nut to crack: deciphering walnut/pecan allergic diagnosis

Published online: October 7, 2020

The increasing prevalence of tree nut allergy worldwide over the past decade and its risk of life-threatening anaphylactic reactions, makes tree nut allergy an important major worldwide health concern. Compounding the problem, the high rates of co-sensitization between tree-nuts lead clinicians to advise patients with confirmed allergy to 1 nut to avoid all tree nuts, impacting on the patients' quality of life. The NUT CRACKER study (NUT Co Reactivity – ACquiring Knowledge for Elimination Recommendations) devised a diagnostic algorithm that accurately distinguished between sensitized individuals and those truly allergic and reduced the need to perform oral food challenges (OFC), which while performed routinely, are not without risk.  

In the current issue of The Journal of Allergy and Clinical Immunology: In Practice, Goldberg et al, prospectively evaluated the diagnostic algorithm for walnut and pecan allergy in a new series of 120 patients. Diagnoses according to the algorithm were made by skin prick testing, utilizing ground walnut or pecan extracts, as well as by basophil reactivity to allergen as assessed by the induction of cell surface markers. Notably, the algorithm utilized the dependent relationship of pecan allergy to walnut allergy, necessitating pecan allergy evaluation only for walnut allergic patients. Validation of walnut/pecan allergic status was performed primarily through an oral food challenge except in cases of recent reactions or if the evaluation uncovered recent walnut consumption. Association of these diagnostic tests with reaction severity was evaluated in the entire NUT CRACKER patient cohort, including the original NUT CRACKER and the current prospective study.

Results of the study validated the algorithm, yielding a decrease in required OFCs of almost 80% with only 2.5% of diagnoses falsely positive without any false negatives. Basophil reactivity to walnut predicted the need for epinephrine during positive walnut OFCs and correlated with the nut eliciting dose. Given the high prevalence of cross-reactivity to several nuts, in tree nut allergic patients, this algorithm will decrease the number of OFC needed to be performed, while maintaining accuracy of diagnosis. The algorithm awaits broader testing across other populations before its widespread adoption into clinical practice.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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