Background Oral factor Xa inhibitors (FXaI) can be administered in fixed doses without the need for routine laboratory monitoring. Anti-Xa assays can estimate anticoagulant effect for specific FXaI's. The aim of this study was to characterize anti-Xa levels in patients taking apixaban or rivaroxaban with major bleeding events. Methods Apixaban and rivaroxaban anti-Xa assays ordered within our hospital system from May 2016 to September 2019 were evaluated. The primary outcome was major bleeding events defined by International Society of Thrombosis and Haemostasis criteria. Median anti-Xa levels for each FXaI were calculated for those with and without major bleeding, as well as those who did and did not receive reversal agents. Results A total of 606 anti-Xa levels were analyzed. There were 146 major bleeding events documented, with the most common site being intracranial (63%). Median anti-Xa levels in patients with and without major bleeding were similar, whereas those on apixaban therapy who received reversal agents typically had higher anti-Xa levels (73 ng/mL vs. 153 ng/mL, p = 0.0019). Factors significantly associated with increased odds of bleeding were an age > 80 years, inappropriately high dosing regimens, and modest anti-Xa levels (100–300 ng/mL) for rivaroxaban specifically. Conclusions Older age and inappropriately high dosing regimens were associated with major bleeding in patients taking apixaban and rivaroxaban. Further investigation into the utility of anti-Xa levels for FXaI is warranted.

Background: Oral direct factor Xa inhibitors (FxaIs) are renally eliminated; thus, acute kidney injury (AKI) may increase the risk for drug accumulation and bleeding. There is minimal data describing the effects of AKI on FxaI anti-Xa levels or clinical outcomes. Objective: To compare anti-Xa level monitoring with standard monitoring in patients who experience AKI on apixaban or rivaroxaban. Methods: This retrospective study included patients admitted within a large hospital system from May 2016 to October 2020. Patients were included if they received apixaban or rivaroxaban prior to AKI. Patients were stratified into 1 of 2 groups: those with anti-Xa level monitoring or those who received standard monitoring. The primary outcome was major bleeding as defined by the International Society of Thrombosis and Haemostasis. Results: A total of 196 patients were included in the final analysis. Major bleeding occurred in 2 patients who received anti-Xa level monitoring, compared with 14 patients who received standard monitoring (2.1% vs 14%; P < 0.01). Variables identified as predictors of major bleeding included a documented history of liver disease (adjusted odds ratio = 3.17; 95% CI = 1.04-9.67; P = 0.04) and antiplatelet use (adjusted odds ratio = 4.18; 95% CI = 1.28-13.7; P = 0.02). Conclusion and Relevance: This is the first study to demonstrate that anti-Xa level monitoring was associated with a significant reduction in major bleeding compared with standard monitoring in patients with AKI who received apixaban or rivaroxaban. The optimal management of antithrombotic medications in patients with AKI and recent exposure to an FxaI requires further investigation.