 This is a multi-center study designed to evaluate the heparin insensitivity of the INRatio Prothrombin Time PT Monitoring System, utilizing an INRatio test strip additionally modified for low sample volume. The INRatio test strip is used for the quantitative determination of PT and International Normalized Ratio INR results in fingerstick blood from subjects on oral anticoagulation therapy OAT with warfarin. This study is designed to evaluate the accuracy of the modified INRatio test strip during heparin-warfarin bridge therapy with unfractionated heparin UH or low molecular weight heparin LMWH, such as enoxaparin or dalteparin. These INR results will be compared to the INR results obtained on plasma from the same subjects as analyzed at a central laboratory with the heparin-insensitive reference method: the Sysmex CA-560 System. The levels of UH or LMWH in the plasma samples will be assessed using activated partial thromboplastin time aPTT and anti-factor-Xa assays respectively. 