Time in therapeutic range: Warfarin anticoagulation for atrial fibrillation in a community-based practice.

OBJECTIVE: To evaluate the effectiveness of an outpatient, nurse-administered warfarin anticoagulation protocol for the treatment of atrial fibrillation, and to identify clinical or biographical data that predict poor international normalized ratio control. DESIGN: Retrospective cohort study. SETTING: St Paul Family Health Network in Brantford, Ont. PARTICIPANTS: A total of 150 patients with nonvalvular atrial fibrillation. MAIN OUTCOME MEASURES: Time in therapeutic range (TTR) for each patient and for the clinic overall. The groups of patients above and below a target TTR of 60% were compared by stepwise binomial logistic regression. RESULTS: A time-weighted average TTR for the clinic was determined to be 58.76%, based on 183 452 patient-days taking warfarin. The regression analysis did not find a statistically significant association between TTR and any predictors. A trend indicating a 5-fold increase in the odds of inadequate anticoagulation was observed in current smokers (odds ratio of 4.71; 95% CI 0.97 to 22.93). CONCLUSION: Compared with data from prospective randomized trials and meta-analysis, the anticoagulation protocol employed at the St Paul Family Health Network produced an average TTR near the lower end of the target threshold. Current smokers might be at greater risk of being below this target.