Patients who have a blood clot are at high risk of having another one, and men have more than twice the risk as women

Patients who have a blood clot are at high risk of having another one, and men have more than twice the risk as women, according to a study in the May 18 issue of JAMA.

While estimates of the overall risk of a thrombotic (blood clot) event recurrence vary, reports on contributing factors are contradictory, according to background information in the article. Knowledge of the risk of a thrombotic event recurrence and its determinants is relevant for clinical policy regarding screening for thrombophilia (increased risk for blood clot), duration of anticoagulant treatment, and treatment strategies in circumstances of increased risk.

Sverre C. Christiansen, M.D., of the Leiden University Medical Center, Leiden, the Netherlands, and colleagues conducted a follow-up study of 474 patients aged 18 to 70 years who had a thrombotic event to determine the risk of recurrence and the effect of several thrombophilic risk factors on the risk of recurrence. The Leiden Thrombophilia Study (LETS) was conducted from 1988 through 1992 and patients were followed-up through 2000.

A total of 474 patients were followed up an average of 7.3 years and recurrent thrombotic events occurred in 90 patients. The researchers "found an annual risk of thrombotic event recurrence of 2.6 percent. The cumulative risk of recurrence was 12.4 percent after 5 years and 16.5 percent after 7 years of follow-up. Although the incidence rate was slightly higher in the first 2 years, at an annual rate of 3.2 percent, the risk of thrombotic event recurrence persisted at a high level of more than 2 percent during the following years."

The risk of thrombotic event recurrence was 2.7 times higher in men than in women. Patients whose initial thrombotic event was idiopathic (unknown cause) had nearly two times the risk of a thrombotic event recurrence than patients whose initial event was provoked. Women who used oral contraceptives during follow-up had a higher thrombotic event recurrence rate than those who did not.

"Solitary laboratory abnormalities appear not to predict the risk of recurrence. Therefore, extensive, if any, thrombophilic work-up after a first thrombotic event is not likely to confer a clinical benefit to the patient. Similarly, a differential treatment with regard to duration of oral anticoagulation in patients with prothrombotic abnormalities does not seem to be rational based on these data. Adequate prophylactic anticoagulation during risk situations for all patients with a history of a thrombotic event may be the most important measure to reduce the risk of a recurrent event. Women using oral contraceptives should be advised to refrain from further use. The decision on optimal duration of anticoagulation therapy after a first thrombotic event will probably need to be based on clinical factors (male sex, oral contraceptive use, and idiopathic first thrombotic event) rather than laboratory abnormalities," the authors conclude.