Rule identifies women who have low risk of vein blood clot recurrence.

A Canadian–led research group has developed and validated a rule that could let half of women with unexplained vein blood clots stop taking blood thinners for life.

These findings were published in The BMJ journal.

Over 1.5 million Canadians will experience a vein blood clot their lifetime, known as venous thrombosis. If part of the clot breaks off and travels to the lungs, it can be fatal. Half of these blood clots happen for no apparent reason, and are known as unexplained or unprovoked clots.

Once an unprovoked vein clot is treated, guidelines recommend that patients take blood thinners for the rest of their lives. If they do not, their risk of having a second clot is 30 to 40 percent in the next 10 years. Taking life–long blood thinners virtually eliminates this risk, but comes at a cost of a 1.2 percent chance of major bleeding per year.

“Patients can get very anxious trying to balance the risks of the treatment with the risks of another blood clot,” said Dr. Marc Rodger, senior scientist and thrombosis specialist at The Ottawa Hospital and professor at the University of Ottawa. “With this rule we can confidently tell half of the women we see that they are at low risk of having another blood clot. This means they can stop taking blood thinners once their initial clot is treated, sparing them the cost, inconvenience and risks of taking life–long medication.”