MONDAY, Aug. 25, 2008 (HealthDay News) -- A new study identifies some women -- but not men -- who might be able to stop taking blood-thinning medication for the clotting condition called venous thromboembolism.
Current guidelines call for indefinite use of a clot-preventing drug, most often warfarin (Coumadin), for many people with the condition. But researchers report that they've identified a group of traits in women that indicate a very low risk of recurrent clots, so that medication might not be necessary after a few months.
The study, published in the Aug. 26 issue of the Canadian Medical Association Journal, found no such indicators of low risk in men with the condition.
The finding applies to what Dr. Marc A. Rodger, a senior scientist at the Ottawa Hearth Research Institute, who led the study, called "out-of-the-blue" venous thrombosis, with no obvious cause of clots in the legs, arms or lungs. In cases where there is a known cause, such as surgery, the risk of a recurrent clot is low and anti-clotting therapy is routinely stopped after a matter of months.
Rodger and his colleagues studied 69 potential predictive factors in more than 600 men and women who had stopped taking an anticoagulant after a first venous thromboembolism. They singled out four of those factors: discoloration, redness or swelling of a leg; high levels of a blood clotting marker, D-dimer; obesity, marked by a body mass index of 30 or higher; and being 65 or older.
Women who had one or none of those factors had a 1.6 percent chance of developing another clot in the next year. Women with two or more had a 14.1 percent one-year risk.
It's a "bit of a mystery" why no predictive factors were found for men, Rodger said. "There are theories about hormonal differences, but none has been proved," he said.
What is known is that while men and women are at equal risk of a first out-of-the-blue venous thrombosis, men are at 1.5 to 2 times the risk of a recurrence, Rodger said. "It's been documented in several studies that men are at increased risk of recurrence," he said.
Between 5 percent and 13 percent of those having recurrent clots die because of them, he added.
Before doctors can start telling women who meet the criterion that they can stop taking Coumadin, Rodger said, "This needs to be validated in a second study which we are currently planning." Those plans call for enrolling 3,000 people in 40 medical centers in Canada, the United States and four other countries.
"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," he said.
Dr. Clive Kearon is a professor of medicine at McMaster University's Michael G. DeGroote School of Medicine, in Hamilton, Ontario, Canada, who wrote an accompanying editorial in the journal. "One would be happy to be able to recommend stopping" blood-thinning therapy, he said, because it increases the risk of major bleeding. "The current recommendation is to remain on long-term therapy, but many patients elect not to do it."
Coumadin is a difficult drug to manage, requiring frequent blood tests and even careful dieting, since green, leafy vegetables are rich in vitamin K, which governs blood clotting.
Some doctors might not wait for the three years needed to get confirmation of the finding, Rodger said. "Oftentimes, patients choose not to take an anticoagulant [blood thinner]," he said. "So, a physician might feel more comfortable to allow women with one or fewer of these risk factors to discontinue the medication."
Learn more about venous thrombosis from the U.S. National Library of Medicine.