Retrospective evaluation of venous thromboembolism: Are all transient provoking events the same?

Objectives: Venous thromboembolism (VTE) provoked by transient risk factors has traditionally been classified as a single entity with lower risk of recurrence. We evaluated the association between different categories of transient provoking factors and the relative risk of recurrence.

Methods: Retrospective evaluation of VTE events in non-cancer patients from July 2011 to December 2012 at two tertiary institutions in Australia with a minimum follow up of 24 months.

Results: 747 VTE cases were identified and following exclusion of cases with mortality within 30 days of presentation (n=26), unprovoked cases (40.2%) had a higher risk of recurrence (4.6 versus 2.3/100 event-years, p=0.01). Provoking factors included surgery (40.4%), injury (16.7%), medical-related factors including non-surgical hospitalisation or active infection (22.0%), travel (13.2%) and oestrogen-related (6.5%). Air travel had the highest recurrence rate of 5.9/100 event-years, comparable to unprovoked VTE. VTE provoked by surgery showed lower recurrence rate at 1.8/100 event-years (p=0.03). 62.5% of patients with provoked VTE recurred with an unprovoked event.

Conclusion: Transient provoking factors for VTE are heterogeneous with varying potency and should not be considered a single entity. The high recurrence rate after travel-provoked VTE suggests that it is a “minor”, if not negligible provoking factor with higher thrombotic predisposition.