Copenhagen University Hospital researchers have found that individuals with AB blood type are 4% more likely to develop blood clots that individuals with O blood type.
Blood clots that form in the lower extremities—called deep-vein thrombosis (DVT)—can become deadly if they break off and become lodged in pulmonary arteries and cause embolisms. Each year, about two million people suffer from DVT, and as many as 200,000 die as a result of complications.
For the study, Borge Nordestgaard and colleagues analyzed blood type and genetic clotting-disorder information on 66,001 individuals who participated in two Danish studies between 1977 and 2010. Specifically, they examined patients with mutations in Factor V Leiden genes and in a clotting agent called prothrombin.
They found that:
Patients with AB blood type had a 4% higher risk of venous-blood clotting compared with participants with O type blood;
Patients with a Factor V—a genetic mutation—were seven times more likely to suffer from a blood clot than those without any variants of the mutation; and
Patients with a clot-favoring prothrombin mutation had an 11-fold increased risk of developing blood clots.
The researchers also found that people with A, B, and AB type blood retain up to 30% higher levels of the von Willebrand clotting factor in the blood compared with O-type people.
Overall, researchers estimated that having an AB blood type contributes to about 20% of the risk for blood clots. By comparison, being overweight accounts for 16%; Factor V accounts for 10%; smoking accounts for 6%; and prothrombin accounts for 1%, respectively (Sifferlin, TIME, 2/4).