Impact of ABO blood group antigens on residual factor VIII levels and risk of inhibitor development in hemophilia A.

Background: The clinical phenotype of hemophilia A (HA) does not always correlate with severity. Similarly, the presence of inhibitors does not necessarily increase the risk of bleeding. This paradox between clinical and laboratory findings may be partially attributed to non-modifiable factors, such as blood group, which is known to influence FVIII levels in healthy individuals. Our aim was to assess the effect of ABO blood group antigens on FVIII levels across the severity spectrum of HA and risk of inhibitor development. Methods: Data of consecutive patients with HA who visited the coagulation unit of a northern Indian tertiary care hospital between 2010‒2021 were reviewed. Patients with missing blood group data, transfusion histories, or baseline FVIII levels were excluded. Results: Mild, moderate, and severe HA was present in 41 (6.9%), 72 (12.2%), and 479 (80.9%) patients, respectively. There were no differences in the FVIII levels among the various blood groups across the HA severity spectrum. Inhibitors were administered to 35 patients (5.9%). In the multivariate analysis, blood group A was an independent risk factor for the development of inhibitors (adjusted odds ratio 2.70, Conclusion: Unlike what is observed in healthy individuals, blood group did not influence residual FVIII levels across the severity spectrum of HA. Patients in group A had a higher risk of developing inhibitors.