What is your preferred assay for assessing dabigatran levels?

The only specific assay that would reflect drug levels is the ecarin clotting time with dabigatran as a calibrator. We used to have this assay in our lab, but due to a lack of use, it was discontinued. The standard thrombin time is too sensitive; however, dilute thrombin time has been used. The mass spec assay would also be reliable and not subject to interferences. The main question is the availability of the assay, which is likely available only in reference laboratories.