Association between group B major ABO ‐incompatible platelet or plasma transfusion and severe allergic reactions: A nationwide haemovigilance analysis suggesting a role for α‐gal syndrome. A Biomedical Excellence for Safer Transfusion Collaborative study

Abstract Background and Objectives Severe transfusion reactions to group B–incompatible platelets and plasma possibly related to the α‐gal syndrome ( AGS ) have been recently described. AGS is a potentially severe Immunoglobulin E mediated allergy to mammalian meat and meat‐derived products associated with tick bites. The involved allergen, galactose‐α‐1,3‐galactose (α‐gal), is antigenically similar to the blood group B antigen. To further assess a potential association between AGS and allergic transfusion reactions (ATRs), we comparatively assessed the frequency of ATRs after plasma or platelet concentrate (PC) transfusion in relation to the degree of ABO compatibility between the recipient and the involved blood component in France. Materials and Methods In France, all transfusions are centrally recorded, and ATR reporting is mandatory. Frequencies of severe ATRs involving PC or plasma in relation to ABO group distributions were analysed between 1 January 2022 and 31 December 2024. Results Among 981,955 PC and 580,230 plasma evaluable transfusions, severe ATRs were significantly higher in group O recipients transfused with group B or AB platelets (relative risk RR: 5.06, 95% confidence interval CI: 3.27–7.83, p < 0.001) and plasma (RR: 2.15, 95% CI: 1.37–3.36, p < 0.001) while not in group A recipients of group B or AB platelets (RR: 0.95, 95% CI: 0.30–2.96) or plasma (RR: 0.92, 95% CI: 0.45–1.88), when compared to ATR rates in all other recipients of PC or plasma, respectively. Conclusion In this national retrospective haemovigilance analysis, group B or AB PC or plasma transfused to group O recipients is associated with an increased risk of severe ATRs . Further studies will establish whether AGS is involved in this increased risk.