Association Between Blood Group O and Bleeding Risk Beyond von Willebrand Factor Levels: A Systematic Review
Underlined: presenting author
Background
Blood group O is associated with lower circulating levels of von Willebrand factor (VWF) and factor VIII (FVIII), raising concern for increased bleeding risk. Whether blood group O contributes to bleeding risk beyond its association with these coagulation factors remains uncertain.
Methods
A systematic review was conducted in accordance with PRISMA 2020 and PRISMA‑S guidelines. PubMed was searched for studies published between January 2010 and November 2025. Observational studies comparing bleeding‑related outcomes in individuals with blood group O versus non‑O blood groups across trauma, obstetric, and surgical populations were included. Two reviewers independently screened studies, extracted data, and assessed risk of bias using the Newcastle–Ottawa Scale. Due to substantial clinical and methodological heterogeneity, findings were synthesized narratively.
Results
Of 63 records identified, six observational studies comprising 92,661 participants met inclusion criteria. Study quality ranged from moderate to high. Associations between blood group O and bleeding outcomes were heterogeneous and context‑dependent. Increased bleeding‑related risk was observed among trauma patients with severe physiologic stress, including higher odds of hyperfibrinolysis (adjusted OR 1.94, 95% CI 1.09–3.47) and massive transfusion (adjusted OR 3.02, 95% CI 1.22–7.49), as well as among obstetric patients with moderate thrombocytopenia (postpartum hemorrhage: adjusted OR 11.0, 95% CI 2.4–49.6). In contrast, studies in unselected obstetric cohorts and elective surgical populations largely reported no significant association. Only two studies measured VWF or FVIII levels, and none incorporated these variables into multivariable models.
Discussion and Conclusion
Blood group O demonstrates a context‑dependent association with bleeding‑related outcomes, functioning as a potential modifier of bleeding risk in high‑risk clinical settings rather than as a universal predictor. Whether blood group O independently increases bleeding risk beyond its effects on VWF and FVIII remains unclear and warrants further prospective investigation.