Perils of Antithrombotic Transitions: Effect of Oral Factor Xa Inhibitors on the Heparin Antifactor Xa Assay.

BACKGROUND: Oral factor Xa inhibitors (OFXais) may interfere with the heparin antifactor Xa (antiXa) assay. The best method to measure heparin activity during the transition from an OFXai to intravenous (IV) unfractionated heparin (UFH) remains unknown. This study aimed to assess the safety and effectiveness of transitioning from an OFXai to UFH. METHODS: A retrospective analysis was conducted of patients with supratherapeutic antiXa levels on UFH who received either apixaban or rivaroxaban within 72 h prior to UFH initiation at NYU Langone Health (NYULH). The primary objective was to identify the incidence of interference on the heparin antiXa assay due to OFXai exposure in the previous 72 h. The secondary outcomes included the indication for transition to UFH and the rate of thromboembolic and bleeding events. RESULTS: A total of 93 patients with supratherapeutic antiXa activity levels with prior OFXai use were reviewed. Moderate renal impairment, defined as CrCl less than 49 mL/min, was present in 67 (72%) patients. The primary indication for transition from OFXai to UFH was in anticipation for a procedure, and it occurred in 37 (40%) patients. There were three major bleeding events and three clinically relevant non-major bleeding events. No thromboembolic events occurred. CONCLUSIONS: This study assessed the prevalence of supratherapeutic antiXa levels and clinical outcomes during the transition from OFXais to UFH. Healthcare systems should develop guidelines to assist clinicians in monitoring antiXa activity in patients undergoing a transition from an OFXai to UFH. It is also important to assess the patient's underlying thromboembolic and bleeding risks.