Blood clots, which form when blood doesn’t flow properly, can happen to anyone, including travelers on long plane rides in cramped seats, women on birth control drugs, or seemingly healthy people with no known risk factors.

Almost half of clots strike patients when they are in the hospital or soon after discharge, ranking them among the most common causes of preventable deaths. Guidelines for preventing clots are in place, yet studies show that 40 percent to 60 percent of patients who would benefit don't receive appropriate treatments. They aren’t given anticlotting drugs because hospitals don’t reliably administer them and patients sometimes refuse them.

Now, many hospitals are intensifying their clot-prevention as they incur more financial penalties in the form of reduced payments from federal and state health agencies if patients develop clots while under their care. Hospitals are using electronic medical records to more precisely identify patients’ risk levels, holding refresher training sessions for nurses, and providing patients with educational materials on the dangers of blood clots.

Clots, known by the medical term venous thromboembolism, typically start in the deep veins of the leg or arm. Those clots are called deep vein thrombosis. When a part of the clot breaks off and travels to the lung, it can cause a pulmonary embolism, or blockage. There are about 900,000 cases of deep vein thrombosis in the U.S. each year, and about 30 percent will become pulmonary embolisms. Of those, about a third are fatal. Democratic presidential candidate Hillary Clinton takes a prescription blood-thinning drug as a result of suffering blood clots in the past.

Normally, when the body is injured, blood clots form to seal small cuts or breaks on blood vessel walls and stop bleeding. But if the clotting process is altered or wrongly triggered, it can cause excessive clotting or prevent clots from dissolving properly. About a third of patients who suffer a clot are at risk for another.

Hospitalized adults with pre-existing conditions such as arthritis, high blood pressure, cancer and kidney failure are about three times as likely to get a life-threatening blood clot than people without such conditions, according to a Centers for Disease Control and Prevention study published last month. The risk of getting a clot also rises with prolonged bed rest, which slows blood flow and causes blood to pool in the limbs. Surgical procedures also can injure veins and cause clots.

To prevent clotting, hospitals follow prevention guidelines typically requiring patients to get three shots daily of a blood thinner like heparin, usually with a small needle injected in the belly. The drug reduces or stops the ability of blood to coagulate into a clot, so doctors and nurses must monitor patients carefully for uncontrolled bleeding.

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