Abstract: Objective The aim of this study is to investigate the effects of ABO blood group and allergy on the susceptibility, disease activity, and related laboratory indicators of Crohn's disease (CD). Methods A total of 207 patients with CD were enrolled in the study. They were grouped by ABO blood group and allergy status, and differences in disease susceptibility, disease activity, and multiple laboratory indicators were compared among different groups. The laboratory indicators included: inflammatory indicators (CRP, ESR, FC, N, L, M, E, B, PLT, NLR, MLR, PLR), nutritional metabolism indicators (ALB, CAR, RBC, Hb), and coagulation indicators (FIB). Results 1.The distribution proportion of blood type AB among patients with CD was significantly higher than that in the general population of Jiangsu region (P<0.012 5). 2. ABO blood group had an impact on specific inflammatory indicators in CD patients: the erythrocyte sedimentation rate (ESR) of patients with blood type O was significantly lower than that of patients with blood type AB (P<0.05), and the faecal calprotectin (FC) level of patients with blood type A was significantly higher than that of patients with blood type B (P<0.05). type A was significantly higher than that of patients with blood type B (P<0.05). 3. Compared with the remission period, the levels of RBC, Hb, ALB, and L in CD active patients were significantly reduced, while the levels of CRP, CAR, N, M, PLT, NLR, MLR, PLR, FC, ESR, and FIB were significantly increased (P<0.05). 4. There was an interaction between ABO blood group and allergy: the RBC and Hb levels in the allergic subgroup of blood type B, as well as the M, MLR, ESR, and FIB levels in the allergic subgroup of blood type A, were significantly lower than those in the non-allergic subgroup of the same blood type; whereas the N and NLR levels in the allergic subgroup of blood type O were significantly higher than those in the non-allergic subgroup of the same blood type. Conclusion ABO blood group is not only associated with the susceptibility to CD but also affects the levels of certain inflammatory indicators. Although allergy does not independently influence the disease activity of CD, it can act as an effect modifier of blood group: it may exert a potential anti-inflammatory effect in CD patients with blood type A, while likely playing a pro-inflammatory role in CD patients with blood type B or O. As a genetic susceptibility marker, the ABO blood group may interact with environmental factors to be involved in the pathogenesis of CD and the shaping of its clinical phenotypes. This finding provides a potential basis for conducting precise prevention and control as well as individualized diagnosis and treatment. In the future, further exploration can be carried out on the customization of blood type-based individualized diagnosis and treatment strategies.

Key words: ABO Blood type, Crohn's disease, Allergy, Fibrinogen, Erythrocyte sedimentation rate, Fecal calprotectin, Intestinal flora