How to deal with interference on heparin anti-Xa activity caused by oral factor FXa inhibitors: communication from the ISTH SSC Subcommittee on Control of Anticoagulation.

Monitoring unfractionated heparin (UFH) to ensure effective anticoagulation may be performed using anti-factor Xa activity (anti-Xa) instead of the activated partial thromboplastin time. However, in patients who have been treated with oral factor (F)Xa inhibitors (apixaban, rivaroxaban, and edoxaban) while switching to UFH therapy, there is a risk that these oral anti-FXa drugs could interfere with UFH-calibrated anti-Xa monitoring. This may lead to inappropriate anticoagulation management. This report of the International Society on Thrombosis and Haemostasis (ISTH) Subcommittee on Control of Anticoagulation summarizes the evidence on the risk of interference from previous treatment with oral FXa inhibitors and UFH anti-Xa after heparin initiation. This communication provides pragmatic recommendations for UFH initiation and management with anti-Xa monitoring after switching from oral FXa inhibitors.