 This is a multi-center study designed to evaluate the accuracy and precision of the INRatio Prothrombin Time PT Monitoring System, utilizing the INRatio test strip newly designed for low sample volume and heparin insensitivity, when used by trained medical professionals for the quantitative determination of PT and International Normalized Ratio INR in fingerstick and venous whole blood from subjects on oral anticoagulation therapy OAT. These results will be compared to those PTINR results obtained on plasma from the same subjects as analyzed at a central laboratory with the Sysmex CA-560 System. 