- The Washington Times - Thursday, July 27, 2006

Patients who have experienced a blood clot in a vein and who have lower levels of thrombin, a blood protein that causes clotting, are at low risk of developing another clot, a new study finds.

“We believe our findings are of major clinical relevance,” because it means such patients can avoid long-term use of anticoagulant treatment and the excess bleeding danger it poses, said Dr. Gregor Hron of the Department of Internal Medicine at the Medical University of Vienna in Austria. He is the co-author of the study published in the July 26 issue of the Journal of the American Medical Association.

The research led by Dr. Hron and Dr. Bernd R. Binder was conducted between July 1992 and July 2005. It included 914 patients, who each had had one venous thromboembolism (VTE), or a clot formation in the deep veins of the legs or in the lungs.

Patients were followed for an average of 47 months after discontinuation of what is known as vitamin K antagonist therapy. Follow-up typically began three to six months after their blood clot occurred.

In their report, the authors pointed out that after ending anticoagulant treatment, “a third of patients experience recurrence of VTE within the next 5 to 8 years.” They said the case fatality rate of recurrence is about 5 percent.

Thrombin is an enzyme formed in shed blood from prothrombin, a protein present in blood plasma. When thrombin reacts with fibrinogen, a chemical substance that exists in blood, it converts fibrinogen to fibrin, which forms the basis of a clot.

“Thrombin generation is key to hemostasis” or the arrest of bleeding, the authors said. So they hypothesized thrombin generation is a marker for risk of recurrent VTE, and they measured it in study participants.

VTE recurred in 100 patients, or 11 percent. The researchers found that patients without recurrent VTE had lower thrombin generation than patients with recurrence.

Just by using a widely available test to measure thrombin, researchers said they were able to identify patients “in whom the long-term risk of recurrent VTE is almost negligible.”

“Considering the incidence rates of severe or fatal hemorrhage related to anticoagulant therapy and the case-fatality rate of recurrent VTE, patients with low peak thrombin generation (less than 400 nM) would almost certainly not benefit from indefinite anticoagulant therapy.”

The new findings could benefit many. About 650,000 Americans suffer from blood clots in the lungs yearly. Most of those cases result from damage of previous clots in the deep veins of the legs.

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