Full Length ArticleIs anti-factor Xa chromogenic assay for Rivaroxaban appropriate in clinical practice? Advantages and comparative drawbacks

- chromogenic assay for rivaroxaban measurement is economically and clinically sound.
- chromogenic measurements of rivaroxaban in our 94 patients overestimated concentrations
- chromogenic LOQ was underestimated and needs on-site re-assessment before use
- rivaroxaban was correctly used in a mere 57% of the cases by the clinicians in our wards

IntroductionNo routine monitoring is required with factor Xa inhibitor rivaroxaban. Yet, its titration must be adapted, and its misuse may lead to increased risk of bleeding; therefore, therapeutic rivaroxaban monitoring might help in specific situations.Material and methodsAs asked by clinicians of our medical center, we measured rivaroxaban plasma concentrations in real conditions of use and checked their corresponding prescriptions. Measurement of 112 samples from 94 consecutive patients was performed with a Biophen LRT® anti-Xa chromogenic assay and compared blindly to the HPLC-MSMS “gold standard” method.Rivaroxaban was effectively given to 80 out of 94 patients but a mere 57% through an adequate prescription (within the scope of indications/titration). All chromogenic measurements were over the pre-specified 30 ng/ml LOQ, whereas only 98 /114 samples had quantifiable rivaroxaban with HPLC-MSMS (LOQ 1 ng/ml). Correlation between the two methods and linear regression were highly significant (p < 0.0001). However, chromogenic values (mean 141.6 ng/ml[96.6]) overestimated HPLC-MSMS values (119.7 ng/ml[79.5]) by 22 ng/ml according to Bland-Altman analysis (p < 0.001). After re-assessing the chromogenic LOQ at 52 ng/ml, 83 quantifiable samples had a mean concentration of 176.9 ng/ml as compared to 158.5 ng/ml with HPLC-MSMS, with no false positive anymore.ConclusionsIn our medical center, rivaroxaban concentrations could be assessed by a rapid chromogenic method. Its pre-specified LOQ proved too high after being checked “on site” against HPLC-MSMS. Prescriptions for rivaroxaban were not optimal. An overestimated LOQ may impair observance monitoring or predispose patients to either risky thrombolysis or otherwise adjournable surgery in clinical practice.