Is Your Blood Type Putting You at Risk for Clots?

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A recent study confirmed the connection between the risk of blood clots and those with an AB blood type.

Blood clots can pose a serious threat to your health when they form in the deep veins of your legs and pelvis – this is known as deep vein thrombosis (DVT). These clots can break free and travel throughout your body, including to the arteries of the lungs, causing a pulmonary embolism (PE) that can block the flow of oxygen to your bloodstream. When this happens, it can cause pain, shortness of breath, or, in some cases, sudden death.

There are a number of factors that can contribute to an increased chance of developing DVT or PE, including old age, obesity, smoking, or being sedentary for long periods of time such as during hospitalization or long-distance travel. Family history and genetic factors, as well as certain gene mutations such as those for Factor V Leiden, can also play a part in DVT and PE risk.

The blood-type study, conducted by Dr. Borge G. Nordestgaard and colleagues at the Copenhagen University Hospital, analyzed information on blood types and clotting disorders in 66,001 people who were followed from 1977 through 2010.

The physicians discovered that people with AB blood type were at a 4 percent greater risk of developing clots in their veins than those with type O blood. Other genetic factors, like Factor V Leiden, led to a sevenfold increased risk of developing clots. However, the AB blood type is far more common than genetic mutations such as Factor V, so it actually accounted for about 20 percent of the risk of developing clots.

Why does the AB blood type increase risk? Blood cells that contain both factors A and B are correlated to the highest levels of von Willebrand factor (VFW), which promotes clotting. People with type O blood have the lowest VFW levels. Types A and B each fall between the AB and O types.

At the moment, it's not clear how doctors will use this information to make decisions about therapies. Most people with type AB blood will probably not develop life-threatening blood clots. However, knowing your blood type can help you know whether you're at increased risk for clotting -- especially if you also have other risk factors, such as obesity, smoking, or taking birth control pills.

If you have any risk factors for developing DVT or PE, talk to your doctor, especially if you are scheduled for surgery or a hospital stay. Your physician can prescribe treatments or recommend prophylaxis to help prevent blood clots from forming. If you're subjected to long periods of immobilization, as in a hospital bed or during a long flight or car ride, be sure to stay hydrated and keep moving to improve your circulation.