The Relationship between the Initial Anti‐factor Xa Measurement and the Duration of Direct Oral Anticoagulant Influence in Patients Transitioning to Heparin

Background Anticoagulation monitoring during transition from direct oral anticoagulants (DOAC) to heparin infusions is a significant challenge. Factor Xa inhibitors influence the heparin calibrated antifactor Xa assay. The University of Virginia (UVA) Medical Center utilized a corrected antifactor Xa assay (c‐AXA) during this transition period, which removes DOAC‐mediated antifactor Xa activity (d‐AXA) and reflects heparin‐specific activity. Currently, the duration of this influence is not well described. Study Objective This study had two aims: to determine if the initial d‐AXA is predictive of the duration of DOAC influence and to further characterize this influence among different patient populations. Methods This retrospective study included adult patients admitted to UVA Medical Center between September 2016 and March 2017, with c‐AXA measurements, who received apixaban or rivaroxaban within 48 hours before heparin initiation. A Pearson correlation test, Kaplan–Meier Survival Analysis, and multivariate linear regression were used to assess the relationship between initial d‐AXA and duration of influence. Results Sixty‐eight patients met inclusion criteria and were maintained on either apixaban (85%) or rivaroxaban (15%) before heparin initiation. The initial d‐AXA ranged from 0.11 to 3.27 IU/ml. The mean duration of influence was 69.3 ± 46.2 hours, with a median duration of 62.7 hours. No strong correlation was identified between initial d‐AXA and duration of influence ( R 2 = 0.124). Presence of interacting medications significantly increased duration of influence (p=0.012). No significant difference in duration of influence existed between patients with normal renal function and those with dynamic renal function (p=0.84), or with body mass index (BMI) greater than 40 kg/m 2 (p=0.16). Conclusions The initial d‐AXA was not predictive of duration of influence in patients transitioning from DOACs to heparin infusion; however, the median duration of influence suggests influence may be present for longer than currently stated in the literature, especially in those taking interacting medications.