Background: Direct Acting Oral Anticoagulants (DOACs) such as Rivaroxaban, are direct inhibitors of factor Xa. With a more stable pharmacokinetic and pharmacodynamics profile, the use of them have been steadily increasing. In Khoo Teck Puat Hospital (KTPH), a 700-bed hospital in the northern area of Singapore, we have seen a similar increase in their use. KTPH laboratory performs routine prothrombin time testing, which may not be suitable for Rivaroxaban measurement.

Aims: The aim of the evaluation is to assess the assay performance of the reagents for the Antifactor Xa assay for Rivaroxaban, to be used in the laboratory.

Methods: The test protocol for the reagent was set up on the CS-2500 automated coagulation analyser (Sysmex Asia Pacific Pte Ltd, Japan). Calibration curves were set for both standard range (12-525 ng/mL) and low range (11-143 ng/mL) analytical measurement. The intra-assay imprecision was evaluated using two levels of the BIOPHEN™ Rivaroxaban Control Plasma and Control Low. A trueness of 146 samples were assessed with results from a referral laboratory.

Results: Intra-assay precision of 8.0% and 2.3% was obtained for Control Plasma 1 and 2 respectively. Results for Control Low 1 and 2 was 6.7 and 2.6% respectively. All results were acceptable and within the manufacturer claim of 15% for control plasma and 20% for control low. Trueness of 146 samples generated a slope of 0.982 with a coefficient determination of 0.962, showing good agreement with the referral laboratory.

Conclusions: Prothrombin time can be helpful and is prolonged if patient has Rivaroxaban in their system. However, the chromogenic method gives a more accurate assessment of the anticoagulant effect of the medication. Although Rivaroxaban does not require routine monitoring or dose titration, it may still be important for laboratories to perform the tests in urgent clinical circumstances.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/an-evaluation-of-the-assay-performance-of-the-antifactor-xa-assay-for-rivaroxaban/