The thrombin time is too sensitive be used to monitor the anticoagulant effect of dabigatran. It may remain prolonged for days after last dose. It's main role is in excluding the presence of an anticoagulant dabigatran effect e.g. in a non-compliant patient or to reassure a surgeon prior to an invasive procedure.

A commercially available dilute TT assay, using a dabiagtran calibrator (Haemaclot) allows you to measure the plasma concentration of dabigatran.

The APTT offers a qualitative assessment of dabigatran anticoagulant effect and is likely to be prolonged by 1.5-2.0 times the APTT upper level at 4 hours

I would recommend LC-MS/MS - We do in the routine clinical practice - range of detection 1-1999 ng/l- It is more precise then Hemoclot TT assay (esp. in low plasmatic concentrations)

Hemoclot is OK. LC-MS/MS may be expensive? TT and APTT may be of some value, but the cut-off should be determined locally since these assays are not standardised.

Perhaps the only specific assay for monitoring Dabigatran, an oral antithrombin agent or other intravenous thrombin inhibitors is the Ecarin Clotting Time or ECT. Other assays such as dilute TT assay, or anti-IIa assays may be used. Assays such as PT, APTT, Heptest are also prolonged in the presence of Dabigatran. The cut off values based on each of these assays have to be standardized. Besides LC-MS/MS method may be used to accurately quantitate the levels of Dabigatran in samples.

The most useful tip is: a significant anticoagulant effect is present if aPTT is above 40 s. In elective surgical patients it is reasonable to wait in order to reduce bleeding risk.

I would not rely on the 40 s cut-off. Different APTT reagents show different sensitivity towards dabigatran. Ratio (for example APTT ratio of 1.5) is also not applicable all over. You have to know what APTT reagent you are using and be aware of its characteristics.