OBJECTIVESTo explore the thrombin generation capacity in patients on warfarin therapy with different prothrombin time international normalized ratio (PT-INR), the capacity in relation to bleeding, and the application of thrombin generation tests to warfarin therapy monitoring.

METHODSSeventy eight blood samples were taken from patients on warfarin therapy for more than 3 months owing to valve replacement or atrial fibrillation. The patients' case history and PT-INR were collected and thrombin generation tests were performed in all samples.

RESULTSPatients were ranked into three groups according to different PT-INR. There were 23 patients in group I with PT-INR from 1.51 to 2.00, 39 patients in group II with PT-INR from 2.01 to 3.00, and 16 patients in group III with PT-INR from 3.01 to 4.26. There were significant differences between each two of the three groups in lag time, peak, and ttpeak (time to peak) (P <0.01). There was a significant difference between group I and group II in endogenous thrombin potential (ETP) (P = 0.0001), but not between group II and group III (P= 0.06). Five patients developed bleeding and their ETP was less than 15% of normal control.

CONCLUSIONIn patients on warfarin therapy, when the PT-INR was more than 3.0, increasing the dose of warfarin doesn' t decrease the thrombin generation, but increase bleeding risk. PT-INR combined with ETP may better reflect patient's coagulation status, therefore be of more significance in preventing bleeding.