Evaluation of MRX PT DOAC as a new screening method for detecting interferences in thrombophilia analyses

BACKGROUND: Direct oral anticoagulants (DOACs) can interfere with coagulation analyses, causing erroneous results such as false-positive lupus anticoagulant and false-normal antithrombin, threatening patient safety when overlooked. A test using a prothrombin time quotient method to detect DOAC presence in plasma samples is now commercially available, the MRX PT DOAC, with the result expressed as Clot Time Ratio (CTR). OBJECTIVES: Evaluate the ability of MRX PT DOAC to identify interfering apixaban or rivaroxaban concentrations, identify non-interfering or interfering patient samples, and detect whether a patient is on DOAC treatment. METHODS: An MRX PT DOAC reference interval was established, and MRX PT DOAC results related to FXa inhibitor concentrations. MRX PT DOAC patient plasma results were related to indications of analytical interference with lupus anticoagulant and antithrombin analyses and with the patients' anticoagulant drug use, according to medical records. RESULTS: The MRX PT DOAC CTR reference interval was 0.98-1.38. MRX PT DOAC apixaban and rivaroxaban interference detection sensitivity was 1.00 (0.96 - 1.0). For subgroups from 315 patient plasma samples, the negative predictive values estimates were 0.84 or above (95% confidence interval minimum 0.64) for excluding analysis interference with the lupus anticoagulant and antithrombin analyses and for excluding DOAC treatment as per medical records. All 9 interference-indicating DOAC samples were identified for the lupus anticoagulant analyses, 5 out of 11 for antithrombin. CONCLUSIONS: The MRX PT DOAC is a potential screening tool for interference. Confirming results in a larger DOAC patient group and further investigating the antithrombin interference detection uncertainty is important.