To investigate the risk of ipsilateral versus contralateral recurrent deep vein thrombosis in the leg.
An open prospective long term follow-up multicentre trial. Patients were followed by frequent outpatient visits at each centre during the first 12 months after inclusion and thereafter annually.
Sixteen hospitals in central Sweden.
A total of 790 consecutive patients with objectively verified first episode of acute deep vein thrombosis and without diagnosed malignant disease were recruited from a randomized study comparing 6 weeks with 6 months of oral antivitamin K therapy as secondary thromboprophylaxis.
Deep vein thrombosis in the contralateral leg was confirmed by venography or ultrasound. With regard to the ipsilateral leg, venography was required.
A recurrent episode of venous thromboembolism was documented in 192 patients after a mean (+/-SD) period of 31(+/-29) months. In 26 additional patients with ipsilateral symptoms the diagnostic critera were not fulfilled. One hundred and eleven patients have deceased and 69 patients withdrew from the study. The 392 patients without recurrent episodes were followed for a median of 96 months with 90% for at least 48 months. An objectively verified recurrent contralateral and ipsilateral deep vein thrombosis occurred in 95 and 54 cases, respectively, and in 41 patients pulmonary embolism was documented. In two patients thromboses with unusual locations were registered. The risk of contralateral versus ipsilateral recurrence was significantly increased with a risk ratio of 1.6 (95% confidence interval 1.4-1.9) in a time to event model. In a multivariate analysis none of the investigated variables were significantly associated with the side of recurrent thrombosis.
The risk of a recurrent deep vein thrombosis is increased in the contralateral leg. This brings into question the importance of an impaired venous flow for recurrent episodes of thrombosis.