An Evaluation of Time to Therapeutic Range of Intravenous Unfractionated Heparin After Transitioning From Direct Oral Factor Xa Inhibitors

Purpose: Direct oral factor Xa inhibitors (Xa inhibitor) may falsely elevate anti-Xa assays, creating a challenge when patients transition from Xa inhibitors to intravenous unfractionated heparin (IV UFH). This study compared the time to therapeutic anti-Xa range in patients transitioning from Xa inhibitors to IV UFH to those not previously anticoagulated and initiated on IV UFH. Methods: This single-center, retrospective study included adults receiving IV UFH from August 2018 through August 2019. The study group received apixaban or rivaroxaban prior to the initiation of IV UFH, and the control group was not previously anticoagulated. The primary outcome was the time to reach therapeutic range. Secondary outcomes included the number of anti-Xa levels drawn to reach therapeutic range, incidence of treatment failure, and incidence of major bleeding episodes. Categorical and continuous data were analyzed with chi-square and Mann-Whitney U tests, respectively. Results: The time to reach therapeutic range was a median of 18.5 hours in the study group (IQR 14.9-26.9) compared to 7.3 hours (IQR 5.9-14.7) in the control group ( P < .001). Two anti-Xa levels were drawn in the study group (IQR 1-4) compared to 1 (IQR 1-2) in the control group ( P < .001). There was no difference in the incidence of treatment failures ( P = .981) or major bleeding episodes ( P = .972). Conclusions: In patients transitioning from Xa inhibitors to IV UFH, the time to therapeutic range was longer and required additional laboratory tests compared to those not previously anticoagulated. Further research is needed to examine the incidence of treatment failures or major bleeding episodes.