This study is to further develop and optimise the design and manufacturing process of a handheld device to monitor and manage Warfarin (blood thinning anticoagulation drug) therapy. The device comprises of a handheld instrument and a disposable test strip and reports how blood coagulation is working in terms of standardised units called International Normalised Ratio (INR). A single drop of fresh whole blood and plasma will be added to the strip and the INR result displayed on the instrument. Blood samples are to be collected from patients attending a hospital based INR clinic who are on Warfarin Therapy. The samples are to be used in a series of experiments in the laboratory to test the Microvisk POC INR Monitors accuracy, precision, stability and robustness.

The number of patients receiving anticoagulation therapy with warfarin and other vitamin K antagonists has been rising in recent years. Increasing life expectancy is increasing the proportion of the population having conditions such as Atrial Fibrillation and venous thrombosis, where primary and secondary prevention of thromboembolic complications are best achieved with anticoagulation.

Unpredictable pharmacokinetics, widespread interactions with drugs and food and the narrow therapeutic window make closely monitoring Vitamin K antagonists a necessity. Portable point of care (POC) coagulometers which measure PT from capillary whole blood and provide an INR reading within a few minutes are already widely available throughout North American and Europe. They give comparable results when compared to laboratory based systems are popular with patients and significantly shorten the duration of clinics. In addition, the United Kingdom Department of Health has been encouraging the use of anticoagulation services in Primary Care Trusts the aim being to provide INR monitoring in community clinics and General Practice surgeries relieving pressure on hospital services and reducing inconvenience for patients.

Although coagulometers are now commercially available the Microvisk INR Testing System has been designed to have advantages, particularly in terms of test robustness, user comfort, ease of use and reduction of user error. The present trial has been designed to develop the second generation Microvisk INR Test System; blood samples will also be used to optimise manufacturing processes and verify the quality of Test Strip Lots.

Inclusion Criteria:

1. Subject is male or female, greater than 18 years of age
2. Subject is receiving warfarin (or warfarin-like) therapy as part of their clinical care
3. Subject is informed and has been given ample time and opportunity to think about his/her participation and has given his/her written informed consent

Exclusion Criteria:

1. Subjects aged <18 years of age
2. Subjects who are unable to give written consent