Presentation Details
| The evaluation of MRX PT DOAC assay for detection of clinically relevant factor Xa inhibitor drug levels Brittany MA Salter1, Karen A Moffat1, 2, 3, Stephen A Carlino3, Liselotte Onelöv4, Sarah Ge1, Marina Atalla1, Raymond Melika1, Saumya Bansal1, Siraj Mithoowani1, Mark Crowther1, 2. 1Department of Medicine, McMaster University, Hamilton, ON, Canada.2Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada.3Hamilton Regional Laboratory Medicine Program, Hamilton, ON, Canada.4Nordic Biomarker, Umeå, Sweden |
Abstract
Introduction: Direct oral anticoagulants (DOACs), including factor Xa (FXa) inhibitors, are increasingly prescribed and do not routinely require laboratory monitoring. Assessment of DOAC levels can be helpful in specific circumstances, especially when deciding on the need for anticoagulant reversal, which is costly and associated with increased thrombotic risk. Patients with DOAC drug levels below 50 ng/mL are unlikely to benefit from anticoagulant reversal strategies, however, drug specific anti-Xa levels are not widely available, limiting clinical utility. We previously showed that the research-use only MRX PT DOAC assay (Nordic Biomarker, Umeå, Sweden) can detect DOAC levels above 50 ng/mL, with a sensitivity and specificity ranging from 75-100%, and 44-86%, respectively. MRX PT DOAC measures the functional effect of DOACs using the clot-time ratio (CTR); the ratio between DOAC-sensitive prothrombin time (PT) and DOAC-insensitive PT. The purpose of this study was to assess the reproducibility of the PT DOAC assay across multiple coagulation analyzer instruments. Methods: This was a retrospective study including 101 clinical samples with known apixaban, edoxaban, and rivaroxaban drug levels for further assessment using the MRX PT DOAC Assay (Table 1). Reagents, calibrators and quality control (QC) were provided by the manufacturer. The assay was run on three coagulation analyzers to determine reproducibility across instruments, including optical based (Werfen ACLTOP 750, Siemens SysmexCS2500) and Viscosity Based Detection (VBD) (Diagnostica Stago STACompact MAX) clot detection systems. The CTR was calculated using Microsoft Excel (Redmond, WA), with a manufacturer reference interval of 0.98-1.38. We calculated the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for a CTR >1.38 to detect a DOAC drug level >50 ng/mL with corresponding 95% confidence intervals (CI). Results: The median sensitivity of the MRX PT DOAC assay to detect DOAC drug levels >50 ng/mL was 66%, 100% and 100% for apixaban, edoxaban and rivaroxaban, respectively (Table 2). The median specificity of the MRX PRT DOAC assay to detect DOAC drug levels >50 ng/mL was 62%, 45%, and 75% for apixaban, edoxaban and rivaroxaban, respectively (Table 2). Conclusion: The PT DOAC assay demonstrates high sensitivity at ruling out clinically significant DOAC drug levels, especially for edoxaban and rivaroxaban. This was reproducible across multiple coagulation analyzers.
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