Timely return of INR values is a problem when INR values are obtained outside the hospital. In some cases, for example, the INR may not be available until late in the evening or the day following the blood draw. If more than 24 hours has elapsed since the blood draw and the time at which a patient would be eligible for randomization the patient will be deemed ineligible for the study. In such cases however, the INR can be repeated (for example at the hospital or clinic laboratory) and if the INR remains above 4.5, the patient can then be enrolled.