Abstract Introduction Calibrated automated thrombinography (CAT) is a sensitive method to assess coagulation. Dabigatran inhibits both free thrombin and the α 2 macroglobulin (α 2 M)-thrombin complex, which results in an erroneously increased peak and endogenous thrombin potential (ETP) without affecting lag time and time-to-peak. The aim of this study was to elucidate the artefacts in CAT when dabigatran is present. Materials and methods Thrombin generation (TG) was measured in vitro by using CAT in the presence or absence of 6 μM idarucizumab in plasma spiked with dabigatran. Additionally, ex vivo measurements were performed in plasmas of 63 patients using dabigatran in the presence and absence of idarucizumab. Results The in vitro experiments confirmed that the ETP, peak and velocity index were artificially increased. This was mainly due to the inhibition of the calibrator by dabigatran and partly due to CAT algorithms. The calibration artefact could be resolved by adding idarucizumab to the calibrator well. However, the second, mathematical artefact remains when dabigatran is present in the TG well. These findings were corroborated by ex vivo experiments i.e. the lag time and time-to-peak were significantly reduced in patients upon addition of idarucizumab, but the ETP and peak were not significantly affected. The velocity index did change significantly, since this is a combination of time-dependent factors and the peak. Conclusions The peak, ETP and velocity index do not represent the anticoagulant effect of dabigatran on TG measured with CAT. The lag time and time-to-peak, however, do reflect the effect of dabigatran. Highlights • Dabigatran causes a counter-intuitive elevation in thrombin generation (TG) • The TG calibrator (α 2 macroglobulin (α 2 M)-thrombin) is inhibited by dabigatran. • α 2 M-thrombin is subtracted from total thrombin to obtain the free thrombin level. • The endogenous thrombin potential and peak do not reflect the effect of dabigatran. • The lag time and time-to-peak do reflect the anticoagulant effect of dabigatran. [ABSTRACT FROM AUTHOR]