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Blood Test Gauges Clot Recurrence Risk

Some patients with deep vein thrombosis need longer drug therapy, study shows

WEDNESDAY, Oct. 25, 2006 (HealthDay News) -- A new blood test can help doctors decide whether to continue anticoagulant therapy for people who have suffered dangerous clots in the legs or lungs, an Italian study indicates.

These clots, called "deep vein thrombosis" (DVT), involve the formation of a blood clot in a deep vein, usually in the lower leg or the thigh. The clots can move into the lungs and cause an often fatal condition called pulmonary embolism. DVTs have come to public attention over the past few years after airline passengers on cramped, long-haul flights developed them in what some have called "economy-class syndrome."

But now, a new test that looks for molecular fragments in the blood called D-dimers may alert doctors to patients most at risk for DVT recurrence.

"We confirmed that if a patent has high levels of D-dimer after treatment, that is predictive of a high risk of recurrence," said Dr. Gualtiero Palareti, professor of cardiovascular disease at University Hospital Saint Orsola in Bologna, and lead author of a report in the Oct. 26 New England Journal of Medicine.

D-dimers are fragments that break off from blood clots, and D-dimer testing is already in widespread use by doctors who treat DVT. "If D-dimer levels are low, the risk of recurrence is low," Palareti said.

Physicians typically treat DVT with anticlotting drugs such as Coumadin (warfarin). Treatment generally lasts about six months, but there is no standard signpost for stopping the medication.

This trial included 608 patients who had been taking anticlotting therapy for at least three months after experiencing a blockage in a blood vessel.

One month after the therapy stopped, tests showed that 223 of them still had abnormally high D-dimer levels.

Anticlotting treatment was stopped for 120 of those patients. Over the next 17 months, 18 of them (15 percent) experienced a second DVT. In contrast, only 3 of the 103 patients who resumed anticlotting therapy experienced clots.

There were 24 recurrent thromboembolisms among the 385 patients with normal D-dimer levels -- an incidence of recurrence of 6.2 percent. That means that patients with abnormal D-dimer levels who stopped anticlotting treatment faced more than double the risk of another DVT compared to patients with normal D-dimer concentrations.

"These patients [with abnormal levels] deserve prolonged anticoagulant therapy," Palareti said.

"D-dimer testing is used frequently in emergency departments and outpatient settings to detect venous thrombosis," said Dr. Jack E. Ansell, professor of medicine at Boston University School of Medicine. While other studies have looked at this issue, "This paper is probably the first with an extensive evaluation for predicting the recurrence of deep venous thrombosis or pulmonary embolism," he said.

The report "will influence the behavior of doctors who treat patients with venous thrombosis," Ansell said. "This test really provides the physician with an estimate of what the likely recurrence rate is in a given patient."

Asked if he would use the D-dimer test for such patients, Ansell said, "I've been using it for a while, because I am aware of preliminary studies indicating its value."

There still are some questions to be answered, he said, including which of the many commercially available D-dimer tests is best. The test used in the Italian study was "relatively insensitive," Ansell said, yet it was still able to detect "a very important difference."

Also, the Italian study included only patients who had experienced a first DVT, Ansell noted. It is not known whether the test would have the same value in patients who had had several clots, he said.

More information

The full venous thrombosis story is available from the U.S. National Library of Medicine.

SOURCES: Gualtiero Palareti, M.D., professor, cardiovascular disease, University Hospital Saint Orsola, Bologna, Italy; Jack E. Ansell, M.D., professor, medicine, Boston University School of Medicine; Oct. 26, 2006, New England Journal of Medicine
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