(EN) The present invention is directed to a kit and a method for a fast and direct determination of the coagulation potential of a sample of blood or plasma utilising a thrombin substrate. The kit comprises at least one activator of the plasmatic coagulation system and a thrombin substrate with a KM preferably less than or equal to 200 µM in a relatively low concentration with respect to the sample whereby the substrate is wholly consumed within 5 to 600 seconds. Observations are made leading to a determination of the maximum rate of substrate consumption.