Once-daily LMWH may also be switched to a twice- daily regimen, particularly if two injections are required to deliver the increase in LMWH dose. Treatment adherence, including compliance, can be dif cult to assess; for example, symptoms of a recurrent DVT may 344 Evidence-Based Medicine [ 1 4 9 # 2 C H E S T F E B R U A R Y 2 0 1 6 ] encourage medication adherence and a return of coagulation results to the therapeutic range. Patient Factors: The most important intrinsic risk factor for recurrent VTE while on anticoagulant therapy is active cancer, with an unexplained recurrence often pointing to yet-to-be-diagnosed disease. Antiphospholipid syndrome is also associated with recurrent VTE, either because of associated hypercoagulability or because a lupus anticoagulant has led to underdosing of VKA because of spurious increases in INR results. Anticoagulated patients may be taking medications that increase the risk of thrombosis such as estrogens or cancer chemotherapy, in which case these treatments may be withdrawn. A retrospective observational study found an acceptable risk of recurrence (8.6%) and major bleeding (1.4%) during 3 months of follow-up in 70 cancer patients with recurrent VTE while on anticoagulant therapy who either switched from VKA therapy to LMWH (23 patients) or had their LMWH dose increased by If there is no reversible reason for recurrent VTE while on anticoagulant therapy, and anticoagulant intensity cannot be increased because of risk of bleeding, a vena caval lter can be inserted to prevent PE.172 However, it is not known if insertion of a lter in these circumstances is worthwhile, and the AT10 panel consider this an option of last resort. *29. 