1.1.1. Conventional follow-up of anticoagulation In this group, the patients are instructed in the use of oral anticoagulants. INR is measured once a month in the laboratory. INR must lie in the therapeutic range designated by the investigative center as a function of the type and the location of the valve and any associated risk factors. If necessary, the family doctor adjusts INR on the day of the blood test and a new measurement is taken 48 hours later if dosage has been changed.