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 PT/INR results obtained on plasma from the same subjects as analyzed at a central laboratory with the Sysmex CA-560 System.

Inclusion Criteria:

• Adults (18 years of age or older);
• Willing and able to provide written informed consent and comply with study procedures;
• Subjects on oral anticoagulation therapy. This inclusion criterion is waived for the 20 normal healthy volunteers who must NOT be on warfarin or any other anticoagulant drug.

Exclusion Criteria:

• Hematocrit less than 25 or greater than 55%;
• Lupus or antiphospholipid syndrome (APS)
• Vulnerable populations deemed inappropriate for study by the site's principal investigator.
• Already participated in this study.

Approximately 210 subjects on OAT and 20 normal healthy subjects not on anticoagulation therapy will be enrolled.