People with non-O blood groups have an increased risk of thrombosis compared to those with blood group 0, a large Scandinavian study confirms.

Writing in Circulation the study authors from the Karolinska Institute said previous studies had linked non-O blood groups to a higher thrombosis risk; however, the magnitude of the risk had not been confirmed.

In the current study of 1.1 million healthy blood donors from Sweden and Denmark non-0 blood groups explained more than 30% of venous thromboembolic events, the research team reported.

People with non-O blood groups had a 92% higher risk of DVT and an 80% higher risk of venous thromboembolism. This equated to an overall population attributable risk of venous thrombosis for non-O blood groups of 36% for DVT, 32% for VTE and 31% for pulmonary embolism, they said.

“ABO blood group may have a role in thrombosis risk assessment and could potentially be added to available clinical prediction systems given the relative ease and robustness of assessing blood group phenotypes and lack of influence of acute phase response on blood grouping” wrote the research team.

They suggested the increased risk of thrombosis may be explained by excess concentrations of or interaction with FVIII and vWF in individuals with non-O blood; or a unified action of immune-dominant blood group antigens present in the lining endothelium of blood vessels, along with the production of vWF by the endothelial cell.