The results of the Prolong study, currently submitted for publication, show that patients with a first unprovoked venous thromboembolic event who have altered D-dimer levels, measured one month after anticoagulation with vitamin K antagonists is stopped, have a high rate of recurrences (about 14%) and a prolongation of anticoagulation is effective in reducing significantly this rate. Those patients with normal D-dimer (about 60% of all patients examined) have a low rate of recurrences (about 5%) and likely a prolongation of anticoagulation in all these patients cannot be recommended.

In line with these results, the Prolong-Two study aims at assessing the predictive role for recurrence of D-dimer levels measured: a) during anticoagulation, b) one month after its withdrawal and c) periodically during follow up.

Patients with a first unprovoked venous thromboembolism (including proximal deep vein thrombosis of a leg and/or pulmonary embolism) which are treated with vitamin K antagonists for not less than 6 months are considered for the study. D-dimer assay is performed during anticoagulation and patients with altered results continue the anticoagulation for 6 more months. Those with normal D-dimer stop the anticoagulant treatment and are again examined one month later. Anticoagulation is resumed for 6 more months in those patients with abnormal D-dimer results but is permanently stopped in those with a normal assay. The latter patients are examined and D-dimer assay performed again every two months to evaluate the natural history of the assay after anticoagulation is stopped and the possible predictive value for recurrence of a change of the assay during follow-up from normal to abnormal results.