Association Between B Positive Blood Type and Clotting Risk
Yes, individuals with B positive blood type have an increased risk of thrombosis compared to those with blood type O, with approximately 1.75-fold higher risk for venous thromboembolism, though this association is weaker for arterial thrombotic events.
Mechanism of Increased Thrombotic Risk
The increased clotting risk in non-O blood groups (including B positive) is primarily mediated through elevated von Willebrand factor (vWF) levels 1, 2:
- vWF levels are approximately 25% higher in non-O blood groups (A, B, AB) compared to blood type O individuals 1
- vWF mediates platelet adhesion and aggregation, and stabilizes factor VIII in plasma, both critical components of the coagulation cascade 3
- ABO blood group antigens are expressed on the N-linked glycan chains of circulating vWF, affecting its proteolysis and clearance 1
Venous Thromboembolism Risk
The association between non-O blood groups and venous thrombosis is well-established 2, 4:
- Overall risk of venous thromboembolism is increased 1.75-fold in non-O blood groups 2
- Individuals with the least O(H) antigen expression (including those with B blood type) may have up to 2.4-fold increased risk 2
- This relationship has been recognized since the 1960s and is now considered a causal association 3, 2
Arterial Thrombotic Events
The association with arterial disease is more modest and less consistent 4:
- Myocardial infarction: Meta-analysis shows pooled odds ratio of 1.28 (95% CI: 1.17-1.40) for non-O blood groups 4
- Ischemic stroke: Pooled odds ratio of 1.17 (95% CI: 1.01-1.35), though this association weakens when restricted to high-quality studies only 4
- The effect on arterial disease is weaker than venous thromboembolism and may be confounded by other cardiovascular risk factors 3
Clinical Implications
Routine screening for thrombophilia based solely on blood type is not recommended 5:
- The absolute risk increase, while statistically significant, is modest in clinical terms 2
- Blood group testing should not replace assessment of established thrombotic risk factors 3
- Consider blood type as one component of overall thrombotic risk assessment in specific high-risk scenarios (pregnancy, oral contraceptive use, major surgery) 5
Important Caveats
- The thrombotic risk associated with B positive blood type is substantially lower than that associated with inherited thrombophilias like factor V Leiden or prothrombin G20210A mutation 5
- Blood group effects may be more clinically relevant when combined with other prothrombotic conditions, such as patent foramen ovale (PFO) 5
- Antithrombotic prophylaxis decisions should be based on established clinical risk factors (surgery, trauma, pregnancy, immobilization) rather than blood type alone 5