Know the warning signs of a deep-vein blood clot, from the January 2016 Harvard Heart Letter

Blood clots can be lifesavers when it comes to healing a wound. But if a clot forms in a vein deep within the body, that's a different story. Known as a venous thromboembolism, or VTE, this type of clot can cause pain, swelling, and redness in an affected limb, and can even be deadly, according to the January 2016 Harvard Heart Letter.

When a clot forms in a leg or arm, it's called deep-vein thrombosis. But the real threat happens if the clot breaks off and travels to the lungs, causing a pulmonary embolism. One or both of these conditions strike at least 900,000 Americans each year, killing at least 100,000. But many Americans don't recognize the symptoms or the serious nature of VTE. Pulmonary embolisms are twice as deadly as heart attacks.

Until recently, doctors thought of VTE as a short-lived condition that could be successfully treated with a brief course of anti-clotting drugs. "We now understand that it's a chronic illness — similar to diabetes and heart disease — that may require lifelong management," says Dr. Samuel Z. Goldhaber, senior cardiologist at Harvard-affiliated Brigham and Women's Hospital. In fact, the same factors that make people more likely to have heart disease, such as high blood pressure, smoking, and obesity, also make them more susceptible to a VTE. Most occur in people ages 60 and older, but younger people can get them, too.

Damage to a blood vessel, from either an injury or surgery, can provoke a blood clot. Being confined to bed during the recovery period leads to sluggish blood flow, further increasing the risk. More than half of VTEs are related to a recent hospital stay or surgery. Undergoing treatment for cancer and prolonged sitting during long-distance travel also increases a person's risk. Between 5% and 8% of people have one of several inherited disorders that make them more prone to clots.

Anyone who is slated for surgery or confined to bed because of an illness or injury should ask his or her doctor about ways to prevent these blood clots from forming. For most people, walking as soon as possible after an operation can lower the risk. Doctors sometimes prescribe anti-clotting drugs for high-risk people after surgery. Another option is graduated compression stockings. These knee-high socks apply pressure to the lower legs, with the greatest pressure at the ankle. They gently increase blood flow from the ankle toward the thigh.

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