The aging of the population and changes in therapy are expected to cause a significant increase in the number of patients requiring anticoagulation therapy. Authors of a British study estimate that the services required to monitor this therapy will increase fivefold over the next decade. Small studies have indicated that patients can successfully use home testing to monitor the International Normalized Ratio (INR) and appropriately adjust oral anticoagulant dosage. Fitzmaurice and colleagues used an English primary care research consortium to conduct a large, randomized trial of self-monitoring of oral anticoagulation therapy.
The researchers studied adult patients who had taken oral anticoagulation for at least one year because of a recognized medical indication. The target INR was 2.5 or 3.5 depending on the medical indication and other factors. A total of 617 participating patients were randomly assigned to intervention or routine care groups. Patients in the intervention group were invited to attend two training sessions covering indications for and the mechanism of anticoagulation; INR concepts and targets; and how to measure, record, and interpret INR results. Patients were further instructed in adjusting medication dosage based on INR results. After training, patients who were judged to be suitable for self-management were issued with home testing equipment and asked to manage their own therapy for one year using INR testing every two weeks. Patients were instructed on quality control measures to be followed in the event of an unusual INR result. Self-management patients were reviewed every three months. Patients in the routine care group attended primary care clinics or hospital anticoagulant clinics to manage therapy. The primary outcome measured was the percentage of time in the therapeutic INR range. Data also were collected on adverse events.
The participants were recruited from 49 general practices, including urban, suburban, and rural areas. The most common cause for anticoagulation was atrial fibrillation, followed by prosthetic heart valves, recurrent pulmonary embolism or deep venous thrombosis, cardiomyopathy, and transient ischemic attacks or strokes. The study contained more men (65 percent) than women. Participants in the intervention group had a younger average age than those in the routine care group (64 versus 66 years). Of 337 patients randomized to intervention, 193 completed the study, compared with 250 of the 280 participants randomized to routine care.
The mean percentage of time within the INR therapeutic range did not differ significantly between the intervention and routine care groups (70 and 68 percent, respectively). A significant improvement in overall control was found in intervention group patients with a target INR of 3.5, but not in other patient groups. Subgroup analysis demonstrated that the greatest improvement occurred among patients in the intervention group whose condition was poorly controlled at entry to the study. There were 16 serious adverse events recorded, equivalent to 2.8 events per 100 patient years in the intervention group and 2.7 in the routine care group.
The authors conclude that self-management is safe and effective for many patients taking oral anticoagulation therapy. They caution that only 25 percent of eligible patients agreed to take part in the study, and that 25 percent of those assigned to intervention did not complete training. Further, 20 percent of those who began self-monitoring withdrew before the year was complete. The reasons for refusal or withdrawal from self-monitoring are unclear, but self-monitoring appears to be a safe and reliable strategy for selected, trained, and highly motivated patients.