Xiaoyan Wang,1,2 Lijia Chen,1 Jiaqi Ding,3 Hongtian Wang,1 Xueyan Wang1,2 1Department of Allergy, Beijing Shijitan Hospital, Capital Medical University, Beijing, 100038, People’s Republic of China; 2Beijing Laboratory of Allergic Diseases, Beijing Municipal Education Commission, Beijing, 100038, People’s Republic of China; 3Department of Otolaryngology, Qingdao Women and Children’s Hospital Affiliated to Qingdao University, Qingdao, Shandong, 0355729, People’s Republic of ChinaCorrespondence: Xueyan Wang, Hongtian Wang, Tieyi Road, No. 10th, Haidian District, Beijing, 100038, People’s Republic of China, Tel +86 13810570961 ; +86 13391836668, Email allergy_wxy@126.com; wht301@263.netPurpose: To investigate the major allergen components associated with birch pollen allergy in northern China and elucidate clinical relevance to pollen food allergy syndrome (PFAS).Methods: Fifty-eight patients were recruited for a cross-sectional study and categorized into two groups: PFAS group and non-PFAS group, as well as apple allergy group and non-apple allergy group. The sIgE levels of birch pollen and its components, namely Bet v 1, Bet v 2, Bet v 4, and Bet v 6, were analyzed.Results: Among 58 participants, 44 individuals (75.9%) reported PFAS. 32 out of 44 (72.7%) participants reported apple allergy. Bet v 1 exhibited the highest sensitization rate at 82.8%, followed by Bet v 2 (29.3%) and Bet v 6 (1.7%). The combined sensitization rate for Bet v 1 and/or Bet v 2 was 93.1%. A total of 77.6% of the subjects demonstrated sensitization to single component, while 19.0% exhibited sensitization to two components. The sIgE levels of birch pollen and Bet v 1 were significantly elevated in PFAS group compared to non-PFAS group (p=0.001, p< 0.001, respectively), as well as in apple-allergic and non-apple-allergic group (p< 0.001, p< 0.001, respectively). The optimal cut-off values for birch pollen and Bet v 1 sIgE were determined to be 7.09 kUA/L (with a sensitivity of 84.1% and specificity of 78.6%) and 5.11 kUA/L (with a sensitivity of 75.0% and specificity of 85.7%) when diagnosing PFAS. In terms of apple allergy, the optimal cut-off value were 9.40 kUA/L (with a sensitivity of 81.3% and specificity of 76.9%) and 6.53 kUA/L (with a sensitivity of 84.4% and specificity of 84.6%), respectively.Conclusion: The predominant sensitization pattern is mono-sensitization to Bet v 1, but when considering immunotherapy, Bet v 2 should also be taken into account. Bet v 1 serves as a valuable biomarker for diagnosing PFAS and apple allergy.Keywords: birch pollen, allergen component, Bet v 1, pollen food allergy syndrome, apple allergy