- MONDAY, Aug. 25 (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.”

More information

Learn more about venous thrombosis from the U.S. National Library of Medicine.