Using the HEMOCLOT direct thrombin inhibitor assay to determine plasma concentrations of dabigatran

The objective of the present study was to assess the suitability of an accurate, sensitive, standardized, chronometric blood coagulation test to determine the anticoagulation activity of dabigatran and to quantify concentrations of dabigatran in plasma. Dabigatran was spiked at increasing concentrations in pooled citrated normal human plasma to measure diluted thrombin time with the HEMOCLOT THROMBIN INHIBITOR assay. Calibration curve linearity, inter-assay and intra-assay precision, and assay accuracy were investigated. Dabigatran stability in plasma and the feasibility of lyophilized dabigatran standards for assay calibration were assessed. Data are presented as back-calculated plasma concentrations of dabigatran using regression analysis. Dabigatran's calibration curve for thrombin clotting time was linear over the concentration range 0-4000  nmol/l (0-1886  ng/ml). The R was 0.99. Total assay imprecision for dabigatran was 4.7-12.0% coefficient of variation, with 1.2-3.1% for intra-run imprecision, 4.0-10.0% for inter-run precision and 0.3-8.3% for between-day imprecision. Assay accuracy was determined at three dabigatran concentrations; deviation from sample target concentrations ranged from -20.7% (100  nmol/l; 47.15  ng/ml) to 5.6% (1500  nmol/l; 707.3  ng/ml). Assay robustness was determined by analysing identical dabigatran samples in two independent laboratories. The mean bias of dabigatran coagulation times between laboratories was 6.6%. The HEMOCLOT Thrombin Inhibitors assay is suitable for determining the anticoagulant activity and calculating plasma concentrations of dabigatran using simple and widely available chronometric coagulation devices. The use of this rapid, established, standardized and calibrated assay should provide accurate and consistent results when assessing the anticoagulant activity of dabigatran.