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tudies assess blood clot prevalence outside hospital, prevention in hospital

July 24, 2007

More cases of venous thromboembolism are diagnosed in the three months following hospitalization than during hospitalization, but less than half of inpatients receive medications to prevent blood clots from occurring, according to a report in the July 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. A meta-analysis of previous studies published in the same issue finds that both unfractionated and low-molecular-weight heparin are effective in preventing blood clots in the legs and lungs of hospitalized patients.

Venous thromboembolism, which includes deep vein thrombosis (blood clot in the deep veins, such as of the legs and pelvis) and pulmonary embolism (clot that occurs in the lungs), is a major cause of complications and death in hospitalized patients, according to background information in the articles. As many as 10 percent of hospital deaths can be attributed to pulmonary embolism. However, previous studies suggest most cases of venous thromboembolism occur out of the hospital.

Frederick A. Spencer, M.D., of McMaster University Medical Center, Hamilton, Ontario, Canada, and colleagues analyzed the medical records of residents from the Worcester, Mass., metropolitan area who were diagnosed with venous thromboembolism during 1999, 2001 and 2003.

"A total of 1,897 subjects had a confirmed episode of venous thromboembolism," the authors write. "In all, 73.7 percent of patients developed venous thromboembolism in the outpatient setting; a substantial proportion of these had undergone surgery (23.1 percent) or hospitalization (36.8 percent) in the preceding three months." Among those patients, 67 percent experienced the condition within one month of their hospitalization. Other major risk factors included active cancer (29 percent) or a previous blood clot (19.9 percent).

Of the 516 patients with venous thromboembolism who had recently been hospitalized, three of five (59.7 percent) received any kind of therapy to prevent the condition while in the hospital. A total of 42.8 percent received anti-clotting medications and an addition 16.9 percent received only non-pharmaceutical prevention methods. "Because most of the cases of venous thromboembolism occurred within 29 days of hospital discharge (and 41 percent occurred within 14 days), it is not unreasonable to assume that some of these cases may have been prevented simply by increased use of appropriate in-hospital deep vein thrombosis prophylaxis (e.g., compression stockings, pneumatic compression devices and, in high-risk patients, anticoagulants)," the authors write.

"Approximately half of the outpatients who experienced venous thromboembolism following hospitalization had a length of stay that was four days or less," they continue. This suggests that patients in the hospital for a short time also should be given preventive therapy. In addition, because the length of hospital stays is decreasing overall, patients may spend more time immobilized at home and therefore may benefit from anti-clotting therapy even after discharge.

In a related paper, Lironne Wein of Monash University and Alfred Hospital, Melbourne, Australia, and colleagues conducted a meta-analysis of previously published randomized controlled trials, all of which compared medications used to prevent venous thromboembolism with each other or with a control group of patients who did not receive prophylactic (preventive) therapy. Thirty-six studies published before June 2006 were included. Fourteen of them compared the drug unfractionated heparin with a control, 11 compared low-molecular-weight heparin to a control, 10 compared the two types of heparin to each other and one compared a drug known as fondaparinux sodium with placebo.

Compared with control groups, unfractionated heparin was associated with a 67 percent lower risk of deep vein thrombosis and a 36 percent lower risk of pulmonary embolism, while low-molecular-weight heparin was associated with a 44 percent lower risk of deep vein thrombosis and 63 percent lower risk of pulmonary embolism. When the drugs were compared with each other, low-molecular-weight heparin was associated with a 32 percent lower risk of deep vein thrombosis and a 53 percent lower rate of hematoma [localized bleeding into or beneath the skin] at the injection site. However, prophylactic therapy was not associated with reduced mortality rates. Fondaparinux sodium was also effective in the prevention of venous thromboembolism.

"This meta-analysis has shown that unfractionated heparin and low-molecular-weight heparin are both associated with a reduced risk of venous thromboembolism in medical patients, with low-molecular-weight heparin being more effective in preventing deep vein thrombosis than unfractionated heparin when considering trials that directly compared the two agents," the authors write. "The unfractionated heparin dosage of 5,000 units three times daily was more effective than the unfractionated heparin dosage of 5,000 units twice daily in reducing the risk of deep vein thrombosis."

"We believe that routine prophylactic anticoagulation has an important place in the medical setting," they conclude. "Although such therapy may not necessarily decrease mortality among hospitalized medical patients, it will reduce the occurrence of deep vein thrombosis and pulmonary embolism and therefore the burden of illness currently caused by these events."

JAMA and Archives Journals