By Jaimie Dalessio
Having AB blood type can be a red flag for venous thromboembolism, or blood clots, in some people, a new study suggests.
Researchers from Denmark analyzed health data and blood samples of 66,001 people, obtained from two Danish studies that followed participants from 1977 through 2010. The researchers looked for blood type and the presence of two genetic mutations, in addition to occurrence of blood clots and heart attacks.
Type AB blood, they found, was a significant risk factor for blood clots, accounting for 20 percent of the risk for venous thromboembolism. And the risk was especially high when those with AB blood type also had one or both of two genetic mutations, called V Leiden and prothrombin. The researchers also considered incidence of heart attack but found no consistent increased risk.
But don't panic if your blood type is AB.
The study's findings are not necessarily new, nor will they change clinical practice, says Neil Blumberg, MD, a pathologist at the University of Rochester Medical Center in Rochester, N.Y. -- at least not for now.
How Blood Types Affect Clotting
Links between blood type, clotting (thrombosis), and its opposite, bleeding, may have to do with a blood component called von Willebrand levels, which are associated with bleeding, Dr. Blumberg explains. People with type O blood have the lowest von Willebrand levels (which make them more likely to bleed); those with AB blood have the highest levels (making them likely to clot); and people with type A and type B blood fall in between.
Many people at risk for thromboembolism are at risk because of underlying disease, age, or the fact that they are in the hospital or just had surgery, and they are probably receiving anti-clotting (anticoagulation) medication without knowing their von Willebrand levels, says Blumberg. Is it something doctors might eventually measure to prescribe more or less medication? Maybe, but that's far off, he says.
Although the Danish study is relevant, he adds, "There's not a lot of data on how to turn it into therapeutic decision-making. Maybe in the future. It adds to a literature that's really just beginning to become to convincing."
For example, a 2011 study from Harvard University found that both men and women with blood type AB faced a 26 percent increased risk of stroke -- which is caused by blood clots that travel to the brain -- compared to those with type O blood. But the researchers couldn't prove cause and effect. A study published earlier in 2011 in The Lancet found that type O blood may offer some protection against heart disease.
In their report, the study authors wrote that the findings suggest blood type should be considered for inclusion in genetic screening for thrombophilia, a genetic predisposition to abnormal blood clotting in the veins.
"Blood Clots More Likely In AB Blood Types" originally appeared on Everyday Health.