Evaluation of Assay Performance Monitoring the New Oral Anticoagulants Rivaroxaban and Dabigatran

Dabigatran etexilate is a new orally direct thrombin inhibitor and rivaroxaban is a new oral direct Factor Xa (FXa) inhibitor. The increasing use of the new oral anticoagulants administered for prevention of VTE in patients after orthopedic surgery creates the need of their measurement in the clinical routine. A modified thrombin time based assay can be used for measurement of thrombin inhibitors like dabigatran and the direct Xa inhibitor rivaroxaban can be measured with a chromogenic anti-Xa assay.

The aim of this study was to evaluate the performance of the two assays on coagulation analyzers using lyophilized calibrators and controls.

The assay for dabigatran measurement is a clotting assay based on the inhibition of a constant and defined concentration of thrombin. Clotting times measured are directly related to thrombin inhibitor concentrations. Calibration of the assay is performed using the lyophilized calibrators with assigned dabigatran values. Lyophilized controls in two ranges with assigned values for dabigatran are measured to calculate recovery and precision.

A one stage chromogenic assay for the determination of Xa inhibitor activity in human citrated plasma is used for rivaroxaban measurement. The assay is based on the inhibition of activated factor × (FXa) by the direct Xa inhibitor rivaroxaban as measured by a chromogenic FXa substrate. Lyophilzed calibrators with assigned rivaroxaban values are used for assay calibration. Controls in 3 ranges are measured to calculate recovery and precision.

Both assays are performed automated using the coagulation analyzers Ceveron alpha, Coasys Plus C and STA Compact with adapted pipetting schemes for the two anticoagulants on each analyzer.

For dabigatran measurement calibration curves in the range of 0–500ng/mL were made on each analyzer and curves with R²=1.0±0.1 were obtained on all analyzers. The recovery of control was ± 10% of target value for all controls on each analyzer.

Precission data of the assay are summarized below:

For rivaroxaban calibration curves in low range 0–150ng/mL and high range 0–500ng/mL were made using two adjusted analyzer settings. Calibration curves with R²=1.0±0.1 were obtained for rivaroxaban in the range of 0–150ng/mL, as well as for the range of 0–500ng/mL on all analyzers. The recovery of control was ± 10% of target value on all analyzers and precision was very good with intra-assay variations between 0.9%-4.2% and inter-assay variations between 1.8–4.9%. The detection limit for rivaroxaban was 10ng/mL using low range calibration curve and 25ng/mL using high range calibration curve.

Our data demonstrate that the diluted thrombin time assay is suitable for mmeasurement of dabigatran and the chromogenic anti-Xa assay is suitable for measurement of rivaroxaban if lyophilized calibrators are used for assay calibration. Optimised pipetting schemes have to be validated for each of the analyzers used in order to obtain results with good precision.

No relevant conflicts of interest to declare.