Evaluation of the MRX PT DOAC assay for detection of clinically relevant factor Xa inhibitor drug levels

BACKGROUND: Although routine monitoring is not needed for direct oral anticoagulants (DOACs), knowing if a clinically relevant DOAC level is present can be critical, especially in cases of severe bleeding or urgent surgery. Rapid assays to exclude these levels are necessary but not widely available. OBJECTIVES: To determine the test performance of MRX PT DOAC for excluding clinically relevant DOAC drug levels. METHODS: The MRX PT DOAC (Nordic Biomarker, Umeå, Sweden) assay measures the functional effect of DOACs using the clot-time ratio, a ratio between DOAC-sensitive prothrombin time (PT) and DOAC-insensitive PT. We conducted a multicenter retrospective study of 152 samples from 151 patients with known DOAC levels to assess whether the MRX PT DOAC assay could exclude clinically relevant drug levels >50 ng/mL and whether test performance differed across coagulation analyzers. To assess generalizability, the assay was run on 4 coagulation analyzers: Werfen ACLTOP 750, Diagnostica Stago STACompact MAX, Sysmex CS2500, and Sysmex CN-6000. RESULTS: The MRX PT DOAC assay had a sensitivity of 100% with a CI of 70% to 100% and negative predictive value (NPV) of 100% (CI: 57%-100%) for edoxaban drug levels >50 ng/mL. For rivaroxaban, sensitivity was 100% (CI: 61%-100%) and NPV was 100% (CI: 5%-100%). For apixaban, sensitivity ranged from 59% to 83% (CI: 41%-93%) and NPV ranged from 0% to 50% (CI: 0%-69%). The specificity of the assay ranged from 61% to 86% (CI: 36%-97%) for apixaban, 36% to 50% (CI: 2%-97%) for edoxaban, and 75% to 100% (CI: 5%-100%) for rivaroxaban. CONCLUSION: The MRX PT DOAC assay reliably excludes clinically relevant levels of edoxaban and rivaroxaban, but not apixaban, across multiple analyzers.