For hazelnut allergy, component testing of Cor a 9 and Cor a 14 is relevant also in birch‐endemic areas
Authors: Riikka Uotila, Petteri Röntynen, Anna S. Pelkonen, Helena Voutilainen, Anna Kaarina Kukkonen, Mika J. Mäkelä
Journal: Allergy (2020)

Diagnosis of nut allergy is usually based on history with a relevant sensitization to the allergen in question and confirmed by allergen challenge. The diagnosis of hazelnut allergy in birch pollen-allergic patients is hampered by cross-reactivity from bich pollen.1, 2 Earlier studies have concluded that Cor a 9 and 14 are the most accurate components for hazelnut allergy diagnostics.3-5 Avoidance of hazelnut and a fear of an allergic reaction may affect the quality of life, therefore improved in vitro diagnosis and in the case of a negative challenge, reintroduction of hazelnuts into the diet is the goal. The aim was to study component diagnostics for severe hazelnut allergy in children and adolescents in a region with heavy birch pollination. Further, we assessed the success of reintroduction in patients with a negative challenge. Eighty-two children and adolescents (aged 1–19 years) with suspected hazelnut allergy were recruited at the Helsinki University Skin and Allergy Hospital. Eligible patients were sensitized to hazelnut (SPT ≥ 3 mm with ground unpeeled nut or IgE ≥ 0.35 kU/L ImmunoCAP whole hazelnut). Specific IgE was measured against whole hazelnut extract; Cor a 1 (PR-10 protein), 8 (lipid transfer protein), 9 (11 S globulin), and 14 (2S albumin); and birch pollen extract. Skin prick tests were performed with ground hazelnut mixed with 0.9% saline and birch pollen extract. At the double-blind placebo-controlled challenges (n = 56), on two days, each patient received 5, 50, 200, and 540 mg hazelnut protein, or placebo (Cumulative dose 795 mg, 6 hazelnuts). At open challenges (n = 26), doses were 5, 25, 50, 100, and 500 mg (Cumulat. 680 mg). Reaction severity was assessed by a threshold-adjusted score in Table S1. A questionnaire of hazelnut reintroduction was sent to the challenge-negative patients. The study (326/13/03/03/2010) was approved by the ethics committee at the Helsinki University Hospital of Children and Adolescents. One of the parents and the patient (≥6 years old) signed written informed consents. See details on methods in the supplemental text. Of the 82 patients, 33 (40%) showed reaction to hazelnut. Of the challenge reactions, 6 (18%) were severe, 7 (21%) moderate, and 20 (61%) mild. Four patients received adrenaline, and three of them needed more than one dose of adrenaline (2 to 3). Birch pollen sensitization (SPT and/or IgE) was present in 68 (83%) patients (sIgE ≥ 0.35 kU/L and/or SPT ≥ 3 mm) (median sIgE 33.8 kU/L [range 0-918], SPT 5 mm [0-13]; Table 1). Correlations between sIgE and SPT to hazelnut, Cor a 1, and birch pollen were moderate to strong (Table S2). Sensitization to Cor a 9 and Cor a 14, n (%) Although the challenge result correlated to some extent with IgE to whole hazelnut extract, moderate-to-severe hazelnut allergy could be most sensitively diagnosed by measuring IgE to both Cor a 9 and 14 (Figure 1; Table 1). Higher levels of specific IgE to Cor a 9 and 14 predicted lower eliciting dose at the challenge: Spearman's rho −0.514, P = .002; and −0.413, P = .017, respectively. Cor a 14 was superior to Cor a 9 in predicting moderate-to-severe reaction (Figure 1). For the cutoff of 2.04 kU/L, the likelihood ratio was 15.9 and the positive predictive value was 75%. Cor a 9 sensitization without Cor a 14 was present in 29 (35%) patients, of whom 25 (86%) were tolerant at the challenge. By combining the IgE levels of Cor a 9 and 14, diagnostic performance was equally good as with Cor a 14 alone (Figure 1; Table 1). Fourty-seven of the 49 challenge-negative patients responded to the questionnaire on reintroduction of hazelnut. Of the respondents, 18 (38%) had introduced hazelnut to their diet (full introduction), 24 (51%) had not actively introduced, but reported not specifically avoiding hazelnut (partial introduction), and 5 (11%) reported avoiding hazelnut carefully (no introduction). This study suggests that asymptomatic sensitization to hazelnut is common and testing for whole extract specific IgE is not a reliable tool when evaluating suspected hazelnut allergy in an area with heavy birch pollination. Serum IgE to whole hazelnut extract and Cor a 1 associate with diagnostic markers of birch pollen allergy rather than hazelnut allergy. Even high IgE to whole hazelnut can be explained by cross-reactivity from birch pollen. In this study, patients with high whole hazelnut IgE—up to 400 kU/L—without concurrent storage protein sensitization tolerated hazelnut. All Cor a 1 monosensitized patients were asymptomatic or experienced only mild oral allergy symptoms. That specific IgE to whole hazelnut correlated strongly with Cor a 1, can be explained by the fact that hazelnut IgE ImmunoCAP is spiked with Cor a 1.6 Therefore, in a birch-endemic region, high serum specific IgE concentration to hazelnut is most often caused by cross-reactivity from birch pollen. The association of Cor a 1 sensitization and oral allergy syndrome is in line with studies from Central Europe and birch-endemic areas from the United States.3, 4, 7 Obviously, measuring Cor a 1 adds no value to the diagnosis of hazelnut allergy. Studies from regions with less birch pollen exposure have reported Cor a 14-IgE as the best diagnostic marker for hazelnut allergy. Our results and the cutoff of 2.04 kU/L are in agreement with these reports.8, 9 However, the diagnostic performance of Cor a 14-IgE was superior to Cor a 9-IgE, which is in line with most previous studies including children and adults both from regions with and without birch pollination.5, 7-10 In our patients, sensitization to Cor a 9, without Cor a 14-sensitization, resulted in moderate-to-severe symptoms only in rare cases. By negative IgE testing for Cor a 9 and Cor a 14, true hazelnut allergy can be most accurately ruled out. In patients with a history of birch pollen allergy or sensitization to birch pollen, hazelnut sensitization is frequent due to cross-reactivity (PR-10 proteins). Sensitization to hazelnut or Cor a 1 is a poor discriminator for hazelnut allergy in this group. This study, however, showed that Cor a 14 and, to a lesser extent, Cor a 9 were a good predictor for true hazelnut allergy. The combination of Cor a 9 and 14 improves allergenic risk assessment. A follow-up on challenges showed that most patients were reassured by a negative challenge and discontinued the unnecessary avoidance of hazelnut. We sincerely acknowledge registered nurses Jonna Harain and Anssi Koivuselkä for conducting patient visits of this study and Helsinki University Hospital Research Funds, Sigrid Juselius Foundation, Pediatric Research Foundation, Finnish Allergy Research Foundation, and Finnish Society of Allergology and Immunology for the financial support. The authors declare that they have no conflicts of interest. Each named author has made substantial contributions to conception and design, and/or acquisition of data, and/or analysis and interpretation of data, and drafted the article or revised it critically for important intellectual content, and given final approval of the version to be submitted. Helsinki University Hospital Research Funds, Sigrid Juselius Foundation, Pediatric Research Foundation, Finnish Allergy Research Foundation, and Finnish Society of Allergology and Immunology supported the study financially. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.