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Canadian Researchers Find Some Women at Lower Risk for Recurrent Thrombosis

A newly published study by researchers at the University of Ottawa (UO) in Canada cites several clinical predictors that can help identify patients at lower risk of experiencing venous thromboses, recurrent blood clots in the veins. These clots and their associated complications are also known as venous thromboembolism (VTE).

VTE has two forms: deep-vein thrombosis (DVT) and pulmonary thromboembolism (PE). DVT occurs when a clot forms deep in veins, usually in the lower extremities (legs, thighs or hip area), and is often associated with pain and swelling. When one of these clots partially or completely breaks free, it can travel through the bloodstream and lodge in the lungs, causing a pulmonary embolism. PE is a serious complication that can result in permanent damage to the lungs and, in some cases, death.

The study results suggest that certain women are much less likely to suffer a successive clot following their initial VTE. Investigators of the study, led by Marc Rodger, MD, MSc, from UO’s Ottawa Health Research Institute, concluded that many of these women could safely be taken off oral anticoagulant therapy, such as warfarin, after approximately six months. 

In addition to having an inherited form of thombophilia such as Factor V Leiden, many other factors need to be considered when assessing the level of VTE risk in patients, including: obesity, long-distance air travel, cigarette smoking, trauma, immobilization and surgery.  For this study, the UO researchers examined 69 factors in 646 men and women who had stopped taking an anticoagulant after their initial VTE. During the average 18-month follow-up period, there were 91 confirmed recurrences of VTE.

Rodger and his team identified four main predictive risk factors in women: discoloration, redness or swelling of the leg; elevated plasma D-dimer levels (an indicator of increased clot formation); obesity, defined as a body mass index of 30 or higher; and being 65 years old or older. Women with none or one of the factors had a 1.6% chance of developing a recurrent clot in the following year; those with two or more factors had a 14.1% risk of recurrence within one year. No predictive risk factors could be identified in the men.
As study authors sought to make sense of the findings, they addressed the lack of predictive factors in men. It is a “bit of a mystery” said Rodger. “There are theories about hormonal differences, but none has been proved.” He also confirmed that while men and women are at equal risk for an unpredicted thrombotic event, men are at a 1.5 to 2 times risk of a recurrent clot. Researchers cautioned that until a predictive tool is discovered for men, all men with an initial VTE should be considered at high risk of a recurrence.

Ultimately, Rodger cautioned against taking female patients off of anticoagulant therapy based on this study alone. “This needs to be validated in a second study, which we are currently planning,” Rodger said. “The study will take about two years to recruit patients and will have a one-year follow-up, so results are expected in three years.” The second study will enroll 3,000 individuals from 40 medical centers in Canada, U.S. and four other countries.

The study, “Identifying Unprovoked Thromboembolism Patients at Low Risk for Recurrence Who Can Discontinue Anticoagulant Therapy,” was published in the August 26, 2008, issue of the Canadian Medical Association Journal.

The UO study was funded by the Canadian Institutes of Health Research and bioMerieux, a laboratory diagnostic technology company based in France. 

Source: The Washington Post, August 25, 2008


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