Microvisk Technologies Ltd designs and develops test systems for monitoring the effectiveness of Warfarin and Warfarin-like medications.

Warfarin and Warfarin-like medications are used to reduce the risk of stroke in people with an irregular heart rhythm (Atrial Fibrillation) or with mechanical heart valve replacements, as well as reducing the risk of recurrent Venous Thromboembolism.

Warfarin dosing needs to be individualized. In order to correctly dose an individual in order to optimize the effectiveness of warfarin, and minimize the risk of bleeding, close monitoring of the degree of anticoagulation is required through regular blood testing. This test is known as PT/INR (Prothrombin Time/International Normalised Ratio). Simply, it is the measure of the amount of time (in seconds) it takes for your blood to clot.

Microvisk Technologies Ltd are developing new anticoagulant test strips for patients on warfarin or warfarin like medications. The blood collected as part of this study will be tested upon Microvisk's second generation Prothrombin/International Normalized Ratio (PT/INR) Test System. The donated blood will be used on ongoing development, validation, verification, and calibration projects. This study is being performed in partnership with the Oxford University Hospital (OUH) and Local Clinical Research Networks (LCRN) Thames Valley Core team, part of National Institute for Health and Care Research (NIHR).

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:

• Currently undergoing Warfarin therapy.
• Over 18 years old

Exclusion Criteria:

A participant is not eligible for participation if ANY of the following criteria are met:

• Participant is <18 years of age
• Participant is unable to give consent
• Participant has been treated with Unfractionated Heparin, or Low Molecular Weight Heparin, within the last 7 days
• Participant has, or is suspected of having, Anti-Phospholipid Syndrome (APS)
• Participant is pregnant, or has been in the past 12 months
• Participant is known to have HIV/AIDS, is a carrier of Hepatitis A, B or C, has had tuberculosis or a tropical disease
• Participant is suspected of intravenous drug use