Key result
A rivaroxaban-specific normalized ratio (NR-rivaroxaban) minimized inter-thromboplastin variability (CV 1.7%–4.7%) compared to INR-warfarin (CV 6.3%–25.1%).
Why the study?
Prothrombin time can monitor rivaroxaban plasma concentration, but responsiveness varies across different thromboplastins, prompting development of a method to reduce reagent sensitivity differences.
Does a rivaroxaban-specific normalized ratio reduce inter-thromboplastin variability compared to INR-warfarin in rivaroxaban-spiked plasma?
Does a rivaroxaban-specific normalized ratio reduce inter-thromboplastin variability compared to INR-warfarin in rivaroxaban-spiked plasma?
A rivaroxaban-specific normalized ratio effectively minimizes inter-thromboplastin variability and correlates strongly with anti-Xa assays, offering a standardized prothrombin time-based monitoring method.
NR-rivaroxaban may improve monitoring consistency; Level 5 data leave open clinical utility pending validation.
Background: The prothrombin time may be used to monitor the plasma concentration of rivaroxaban. However, there is variability in the responsiveness of rivaroxaban to different thromboplastins. We aimed to develop a rivaroxaban-monitoring method using the prothrombin time to reduce the differences in the sensitivity among reagents.Methods: Rivaroxaban-spiked pooled normal plasma at a 0–1000 ng/ml concentration was used to generate a rivaroxaban-adjusted sensitivity index (SI) values, and was tested with three thromboplastins. The warfarin-adjusted international sensitivity index (ISI-warfarin), rivaroxaban-adjusted sensitivity index (SI-rivaroxaban), international normalized ratio (INR) calculated with ISI-warfarin, normalized ratio (NR) calculated with SI-rivaroxaban, and their coefficient of variances (CVs) were compared. The NR-rivaroxaban value was compared with the results of an anti-Xa assay.Results: The ISI-warfarin and SI-rivaroxaban using different thromboplastins were 1.02 and 1.88, respectively, with Thromborel S, 0.90 and 1.00 using Recombiplastin 2G, and 1.30 and 1.15 using Neoplastin CI-plus. Between-thromboplastin variability expressed as CV were 6.3%–25.1% when expressed as INR-warfarin and 1.7%–4.7% when expressed as NR-rivaroxaban. CVs for the NR-rivaroxaban with another laboratory were significantly lower than those for INR-warfarin. Anti-Xa assay v NR-rivaroxaban correlation coefficients were 0.97–0.99.Conclusion: Using a rivaroxaban-specific NR effectively minimises inter-thromboplastin variability. By utilizing a NR-rivaroxaban, standardized prothrombin time results could be rapidly obtained, especially useful in standardizing the therapeutic effect of rivaroxaban.
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Kim et al. (2019) studied this question. Rivaroxaban-adjusted normalized ratio (NR-rivaroxaban) vs. INR-warfarin was evaluated on Between-thromboplastin variability (coefficient of variance). A rivaroxaban-specific normalized ratio (NR-rivaroxaban) minimized inter-thromboplastin variability (CV 1.7%–4.7%) compared to INR-warfarin (CV 6.3%–25.1%).
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