The INR--a help or a hindrance to warfarin dosage?

We have examined the INR values of 128 warfarin patients obtained by four different techniques in common use in Scotland namely venous and capillary. Thrombotest and venous and capillary Prothrombin Time (PT). The PT INRs were carried out using Manchester Reagent thromboplastin. Discrepant INR values were obtained. The mean Manchester venous INR values were lower than those obtained by the other three methods (p less than 0.0001). This suggests that patient's dosed by reference to Manchester venous INR are liable to receive more warfarin than those dosed by the other methods.