A nationwide Belgian survey on the influence of the new oral anticoagulants dabigatran and rivaroxaban on commonly used coagulation assays

Background: The new oral anticoagulants dabigatran etexilate (direct thrombin inhibitor, Pradaxa®, Boehringer Ingelheim) and rivaroxaban (direct factor Xa inhibitor, Xarelto®, Bayer) have been in clinical use for a few years for the prevention of thromboembolic events after elective hip- or knee-replacement surgery and for the prevention of stroke and systemic embolism in patients with atrial fibrillation. Although these agents do not require monitoring, their presence can significantly influence coagulation assays, potentially leading to incorrect interpretation of test results. Aims: The Belgian national External Quality Assessment Scheme for blood coagulation organized a survey to investigate and illustrate to the clinical laboratories how these drugs affect their routine coagulation assays. Methods: All Belgian clinical laboratories routinely performing coagulation testing (n = 192) received five lyophilized plasma samples in April 2012. These samples consisted of a normal plasma pool spiked with dabigatran or rivaroxaban to the following final concentrations: 0, 100 ng/mL dabigatran, 250 ng/mL dabigatran, 120 ng/mL rivaroxaban, and 290 ng/mL rivaroxaban. The samples were purchased from Hyphen BioMed (Neuville surOise, France). Participants were requested to determine the following coagulation assays: prothrombin time (PT, seconds,% and INR), activated partial thromboplastin time (aPTT, seconds and ratio), fibrinogen and antithrombin. They were also required to mention the reagent and analyser used. Method-specific medians and robust standard deviations were calculated for all methods with ≥ 6 reported results (method of Tukey). Differences between methods were assessed by means of non parametric statistics (Wilcoxon test). Results: All but three laboratories participated in the survey (response rate of 98.4%). PT and aPTT: Both, dabigatran and rivaroxaban significantly prolonged the PT and aPTT in a concentration- and reagent-dependent manner. The PT was more influenced by rivaroxaban than by dabigatran, while the aPTT was more influenced by dabigatran than by rivaroxaban. There was a wide variation in responsiveness between reagent/instrument combinations. The PT reagents Neoplastin CI Plus and Neoplastin R (Diagnostica Stago, Asniéres sur Seine, France) were the most sensitive to rivaroxaban and the reagents Innovin and Thromborel S (Siemens, Marburg, Germany) the least sensitive. The aPTT reagents most and least sensitive to dabigatran were CK Prest (Diagnostica Stago) and Actin FSL (Siemens). Converting PT results to INR did not reduce but even increased the variability between reagents. Fibrinogen: Rivaroxaban did not influence the determination of fibrinogen but the presence of dabigatran led to a falsely reduced fibrinogen concentration when measured with a low thrombin concentration reagent. Antithrombin: The presence of dabigatran caused an overestimation of the antithrombin level when measured with an assay based on thrombin inhibition while the presence of rivaroxaban caused an overestimation of the antithrombin level when measured with an assay based on FXa inhibition. Summary/Conclusions: This study demonstrates that the influence of dabigatran and rivaroxaban on the routine coagulation assays used in Belgium largely depends on the reagent/analyser combination used and the drug concentration. All laboratories received a full report of the results in order to draw attention to the importance of careful interpretation of coagulation test results in patients taking dabigatran or rivaroxaban