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  • Title: [Accuracy and reliability of international normalized ratio (INR) in monitoring of warfarin--comparison in the sensitivity to extrinsic coagulation factors between PT (INR) and TT (INR)].
    Author: Sakayori T, Naito S, Yoshida M, Kumano O, Kato N, Okuda M, Ieko M.
    Journal: Rinsho Byori; 2010 Aug; 58(8):779-85. PubMed ID: 20860170.
    Abstract:
    Prothrombin time (PT) is widely used as the monitor of oral anticoagulant therapy using ISI/NR system which WHO recommended. However, a main clinical usefulness of an Owren-type combined reagent (TT) also remains in the monitoring of warfarin in Europe and Japan. Recently, a TT reagent utilizing a recombinant bovine tissue factor (TF) expressed by silkworm-baculovirus system has been developed. The purpose of this study is to investigate the sensitivity to coagulation factors (FII, FV, FVII, FX) of PT (rabbit brain and recombinant human) and TT (bovine brain and recombinant bovine) in INR, and the correlation among those reagents using 53 plasma samples from patients treated with warfarin. The INR results were calculated using a certified INR calibrator, "AK-CALIBRANT", according to the method of "Direct" INR determination. The sensitivity to FII, FVII and FX of those reagents results similar behavior in INR, but the sensitivity to FV of PT reagents were generally higher than that of TT reagents. The correlation coefficient between recombinant PT and recombinant TT was 0.979. There were a good agreement between two TT reagents (bovine brain and recombinant bovine) in INR (r = 0.998). It was apparent that a variance between PT and TT was dependent on the sensitivity to FV level during the course of warfarin treatment in a clinical case. In conclusion, PT and TT reagents gave generally acceptable correlation in INR, and our results indicate that the Owren-type TT reagent is also well suited for monitoring warfarin using local INR calibration according to WHO recommendation.
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