Comparison of Prothrombin Time INR Derived From Point-of-Care and Laboraotry Test According to Fibrinogen Level

Abstract 4325

Coumarin-derived anticoagulants such as warfarin inhibit the vitamin K expoxide reductase (VKORC1) and block vitamin K cycle rendering coagulation factors II, VII, IX, X left in functionally null state (PIVKAs). Because of the narrow therapeutic range of warfarin, prothrombin time standardized into international normalized ratio (INR) should be frequently measured to prevent unwanted bleeding or recurring thrombosis. Point of care (POC) tests for patient self monitoring of anticoagulation was developed with the intention that more frequent monitoring of would enhance the compliance of the patients and prevent overdose. The accordance between results derived from these POCs tests and clinical laboratory tests has been repeatedly reported and the patients self monitoring strategy is now generally accepted as a reliable way for maintaining safer anticoagulation therapy. However, we pointed out that the POC test, especially CoaguChek (Roche) wide in use domestically, can show different correlation pattern with laboratory tests according to fibrinogen level, because the assay principle of the POC test is basically measuring thrombin activity. We found negative bias of POC INR compared with laboratory test from specimen with fibrinogen level lower than 130 mg/dl while positive biases were observed from that with fibrinogen level higher than 130 mg/dl. The difference in INR range from −0.7 to 1.7 and the maximum differences in both directions were observed in specimen with INR above 3.0, that is exceeding therapeutic range. These results suggest that patient selection according to fibrinogen status should precede the implementation of patient self monitoring and periodic laboratory tests and comparison with POC results should be continued as before the initiation of self monitoring.