Oral Anticoagulation Thresholds

Background Monitoring patients on oral anticoagulation is essential to prevent hemorrhage and recurrent thrombosis. We studied tissue factor–induced whole-blood coagulation in patients on warfarin therapy with similar international normalized ratios (INRs). Methods and Results Contact pathway–suppressed whole-blood coagulation initiated with tissue factor was studied in 8 male subjects (group W) and in 1 individual multiple times (subject A). Coagulation profiles for group W showed that subjects with similar INRs had widely varying clot times (6.2 to 23 minutes) and thrombin–antithrombin III (TAT) profiles with rates of 25 to 40 nmol · L−1 · min−1 and maximum levels varying from 192 to 349 nmol/L. The normal control group exhibited clot times of 5.7±0.3 minutes and TAT rates of 57±13 nmol · L−1 · min−1, reaching maximum levels of 742±91 nmol/L. Subject A, who was stably anticoagulated at an INR of 2.1±0.4 for 6 months, had widely ranging profiles with clot times of 9.0 to 22.7 minutes, TAT maximums varyin...