Men with a
blood clot history are more likely to suffer a recurring clot than women
with the same background, according to a review of recent studies.
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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