THURSDAY, July 27, 2006 (HealthDay News) -- Men are 50 percent more likely than women to develop another blood clot after having a first episode of deep venous thrombosis (DVT), researchers report.
DVT involves the formation of a blood clot in a deep vein, usually in the lower leg or the thigh. These clots can move into the lungs and cause an often fatal condition called pulmonary embolism. DVTs have come to public attention over the past few years after airline passengers on cramped, long-haul flights developed them in what some have called "economy-class syndrome."
Now, a new review of the data "provides pretty strong evidence that men have a higher risk of having another episode of venous thrombosis than women," according to study co-author Dr. Clive Kearon, head of the clinical thrombosis unit at McMaster University, in Hamilton, Ontario, Canada.
The overall frequency of recurrent blood clots is 25 percent after five years, the researchers noted. Their report is published in the July 29 issue of The Lancet.
However, it's not clear whether the finding should translate into different treatment for men and women, Kearon said. "It looks to be a real association, but it's not an overpowering association that says that men should necessarily be managed differently than women when it comes to deciding how long they should be receiving anticoagulation treatment," he said.
In their review, Kearon and his colleagues analyzed studies of both men and women being treated for either DVT or pulmonary embolism. The researchers looked at rates of the recurrence of blood clots after the patients had stopped taking anticoagulant medication.
The researchers pored over data from 15 studies that included more than 5,400 patients. Half the patients were male and half female. They found that 816 patients had recurrent blood clots. Of these, 64 percent were in men and 36 percent were in women.
Current evidence suggests that people who develop DVT for no apparent reason need long-term, indefinite anticoagulation (blood thinning) therapy, Kearon said. "This study tells us that when we are weighing the risks and benefits of this therapy, one of the factors that we should take into account is whether the person is a male or a female," he said.
The reason for this gender difference isn't clear, Kearon said. "We do not have a good explanation for the finding. The lack of a good explanation makes us a little more careful about overstating the importance of the finding," he said.
One expert thinks these findings alone should not be the basis for changing what physicians are doing now to prevent recurrent DVT.
"The findings are what everyone suspected, that men have a slightly higher risk of recurrent DVT," said Dr. Suresh Vedantham, an associate professor of radiology and surgery at Washington University Medical School, in St. Louis.
Vedantham said it's unclear how these findings might affect treatment. There is a debate among doctors about how long someone should remain on anticoagulant therapy after a first episode of DVT.
"This is a significant question," he said. "For example, if you don't anticoagulate someone and they have a recurrent event and it turns out to be a pulmonary embolism, it can be fatal. But if you do put someone on blood thinners long-term, there are risks of bleeding complications."
The question is whether you put men on anticoagulants longer, Vedantham said. "But in terms of knowing what to do right now, we need more studies," he said. "Right now, in terms of specific changes in practice, I don't think this study is quite enough to really mandate a change in practice."
For more on deep vein thrombosis, head to the U.S. National Heart, Lung, and Blood Institute.