9. Abstract Title: Measurement of anti-factor Xa direct oral anticoagulant levels in the plasma samples from the perioperative anticoagulant use for surgery evaluation (PAUSE) study

Abstract

Rivaroxaban and apixaban are the most commonly used anti-factor (F) Xa direct oral anticoagulants (DOAC), with indications for prevention of stroke in non-valvular atrial fibrillation as well as treatment and prevention of venous thromboembolism. However, lacking is a detection method to quantify levels of these DOACs with relative ease and accuracy. We report a new assay that measures anti-FXa DOAC levels in plasma and whole blood. This is achieved by measuring the rate of prothrombin cleavage by residual FXa activity, which is inversely proportional to the DOAC levels present. Standard curves were generated by adding known levels of DOAC into normal pooled plasma, which demonstrates linear dose-response between 0 and 5 nM for rivaroxaban and between 0 and 10 nM for apixaban. Corn trypsin inhibitor did not affect this assay. Generation of standard curves using individual plasma samples demonstrated consistency and reproducibility. With whole blood (2 μL), the dose response to the DOACs was similar with linearity between 0 and 1 nM. To validate the assay for measuring DOAC levels in clinical plasma samples, 24 samples were measured per DOAC without any dilution or modification of the sample. Of the 24 samples, 15 and 9 of the samples were within acceptable range (i.e. no greater than 100% and no less than 20% of total rate change) for rivaroxaban and apixaban, respectively. Thus, the assay is ideal for rapidly and accurately measuring DOAC levels in plasma and blood, demonstrating its potential for point-of-care applications.