Utilization of international normalized ratio-derived formula to predict plasma rivaroxaban level-Validation study and real-world experience.

Introduction: Specific assays of plasma rivaroxaban level are not always readily available with short turnaround time, which hamper the management of urgent clinical situations. In this study, we aimed to build a predictive formula of plasma rivaroxaban levels from international normalized ratio (INR) value and validated in real world clinical situations.

Methods: Ninety-four patients who were taking rivaroxaban participated in the study. Patients were randomized into testing cohort and validation cohorts. The prediction formula was built from the testing cohort and then validated in validation cohort. The predictive performance was further validated on real-world clinical requests.

Results: The root mean square error (RMSE) of the predictive formula for the testing and validation cohorts were 61.81 and 69.32 ng/mL, respectively. The sensitivity and specificity for the formula to predict the threshold plasma rivaroxaban level of 75 ng/mL were 95% (95% CI: 85.4%-100%) and 87.5% (95% CI: 71.3%-100%), respectively, in real-world clinical situations.

Conclusion: Plasma rivaroxaban level of threshold level of 75 ng/mL can be calculated from prediction formula by INR value with satisfactory accuracy and it can be used to guide the decision for reversal.