Drs. Cattaneo and Mannucci hypothesize that a subclinical post-thrombotic syndrome increases the risk for ipsilateral thrombotic recurrence. Their hypothesis is not supported by our data. First, the risk for recurrent deep venous thrombosis depended on the presence or absence of risk factors, whereas the occurrence of post-thrombotic sequelae was most strongly related to recurrent ipsilateral thrombosis. Second, among the 63 patients with recurrent deep venous thrombosis, 35 cases (56%) involved the ipsilateral leg and 28 (44%) involved the contralateral leg. If a subclinical post-thrombotic syndrome would be a major risk factor for recurrence, one should expect that this difference would be far more pronounced. Therefore, we still believe that prevention of recurrent (ipsilateral) deep venous thrombosis (rather than aggressive fibrinolytic therapy) might be a key to decreasing the incidence of the post-thrombotic syndrome.

With regard to the issues raised by Drs. White and Romano, we could not observe a difference in risk for recurrent thromboembolic disease among patients on the basis of age. Although variables were entered stepwise into the Cox proportional-hazards model, only the hazard ratios observed in the final model were reported, thereby enabling the desired comparisons. Data on the association of factor V Leiden mutation and the risk for recurrence have been published elsewhere [1]. The optimal treatment of patients with different risk factor profiles is unknown; further studies in this area are needed.