In a metanalysis of published papers, researchers from Canada and Australia determined men have a 50 percent greater risk of suffering a recurrent venous thromboembolism -- a potentially fatal condition consisting of either deep-vein thrombosis or pulmonary embolism -- than women. A pulmonary embolism occurs when a clot forms, detaches from the vessel, travels to the lungs and and lodges in the pulmonary arteries.

   "It confirms there is pretty strong evidence of an association," said senior author Dr. Clive Kearon, associate professor of medicine at McMaster University in Ontario, Canada. The research may also influence how men are treated for blood clots, he added.

   The research, led by Dr. Simon McRae of Queen Elizabeth Hospital in Australia, will appear July 26 in The Lancet. 

   The research team analyzed 5,416 individuals in randomized and observational studies worldwide, all of whom had experienced a blood clot but recently stopped treatment. Of the 816 participants in the group who had blood clots, 523 were men and 293 were women.

   The average patient with venus thromboembolism has a 10 percent risk of clot recurrence in the first year after stopping treatment; after five years, it is about 25 percent. 

   In this metanalysis, the authors found the risk in men within one year was 16 percent for a recurring clot, and for women it was 6 percent. 

   Two previous studies have suggested men had a higher risk for recurring clots than women; however, others have found no association. 

   It's hard to pinpoint the exact prevalence of venous thromboembolism, but  the Cleveland Clinic estimates more than 250,000 cases are diagnosed annually in the United States. At least 50,000 of these cases are fatal.

   Although the study authors also hoped to discover why this gender difference occurs, "no earth-shattering hypotheses" emerged, said study author Dr. Jeff Ginsberg, a professor of medicine at McMaster University.     

   Ginsberg and colleagues plan to analyze the biochemical changes that occur in the body following a blood clot event. 

   It's possible women have protective chemicals in their blood against clots, or conversely, men have chemicals that makes them more susceptible, Ginsberg said. 

   Likewise, there could be confounding -- or complicating -- factors that influenced the results, Kearon said. The reduced risk of recurrent blood clots in women did not seem to be associated with estrogen treatment or pregnancy, the authors wrote. However, hormones might have a "transitory effect" on lowering blood clot risk, they acknowledged.

   The findings could become part of the conversation physicians have with their patients, Kearon said. Often, deciding whether to continue oral anticoagulant treatment is weighing risks and benefits, as well as the patient's like or dislike of the treatment. 

   Although anticoagulants are effective, they can cause fatal bleeding. 

   Based on this research, a male might want to consider staying on longterm therapy, whereas a female might feel more comfortable stopping the blood-thinning medication, Kearon said.

   However, Richard White, a professor of medicine at University of California at Davis, will not tell his male patients who have had a blood clot that their risk of recurrence is higher than women. 

   Although this recent metanalysis is a worthy investigation, it's "a little bit strange" that the actual incidence of blood clots in men and women are equal, but the rate of recurrence is not, White said.

   "We need to dig down a little bit further," he said. 

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