Thrombin generation and coagulation factor activities: evaluation and comparison with the international normalized ratio.

Oral anticoagulation therapy is monitored effectively by the international normalized ratio (INR). However, INR is perhaps not optimal in predicting risk of complications. Other more sensitive methods have been suggested. The aims of this study were to estimate the variability and association of calibrated automated thrombin generation (CAT) and clotting activity of coagulation factors II, VII, IX and X and to compare these parameters with the INR measured in a central laboratory as well as using portable coagulometers. Twenty-four patients on stable oral anticoagulation therapy with coumarins were followed prospectively for 6 weeks. A mixed effect model was used for the statistical analyses. The CAT and activity of coagulation factors II, VII, IX and X showed no significant difference in variability over time. Approximately 50% of the total variability of the CAT and coagulation factor activities was displayed as variation in the INR. The remaining variability was displayed as 'within patient variation'. The CAT and coagulation factor activities were significantly associated with the INR. In conclusion, neither CAT nor coagulation factor activities seem to provide additional information about the biological variation; however, larger clinical studies are needed to investigate the ability to predict complications in individual patients on oral anticoagulation therapy.