Abstract Number: PB0699
Meeting: ISTH 2020 Congress
Background: Anti-Xa assays are the standard of care for the estimation of plasma levels of anti-Factor Xa (FXa) inhibitors. Laboratories have to establish a calibration for each of the anti-FXa-inhibitors, which is expensive and cumbersome to handle.
Aims: The aim of this study is to show that the DOAC plasma levels can be estimated independently from the anti-Xa-assay and the specific calibrator used in the test. It would be beneficial to compare DOAC levels based on their actual anti-Xa activity rather than the non-comparable mass concentrations.
Methods: A total of 303 blood samples containing apixaban (n=122), edoxaban (n=85) or rivaroxaban (n=96) from patients at defined time points after DOAC intake were included into the analysis. Plasma levels were analyzed using six anti-Xa-assays were calibrated against each available anti-Xa calibrator. A consensus value for each analyte and sample was calculated from all combinations of assay and calibrators. Results from individual combinations of assays and calibrators were compared to the consensus value.
Results: The variation of results between different assays and calibrators does not exceed the measurement error of anti-Xa assays. Furthermore, the bias obtained by using the “wrong” calibration (e.g. determination of an edoxaban level using an apixaban calibration) is constant between assays and calibrators using correction factors.
|calibrator (column) analyte (rows)||apixaban||edoxaban||rivaroxaban|
[Correction factors for the determination of DOAC levels using a non-corresponding analyte and calibration]
Conclusions: DOAC levels can be determined with just one calibrator using correction factors for a non-corresponding drug. While apixaban and edoxaban show similar anti-Xa activity based on their mass concentration, rivaroxaban differs significantly.
Based on our data it would be possible to define a standardized calibrator for all DOACs using a concept similar to LMWHs. It is conceivable, that comparing DOAC levels based on their anti-Xa activity is preferable over a comparison based on mass concentration. As anti-Xa assays are incapable of identifying a DOAC in a sample, providing solely the anti-Xa activity constitutes a superior approach.
To cite this abstract in AMA style:Pfrepper C, Siegemund A, Metze M, Petros S, Siegemund T. On the Measurement of Direct Anti-Xa-Inhibitors [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/on-the-measurement-of-direct-anti-xa-inhibitors/. Accessed December 3, 2021.
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