Cost efficiency of anticoagulation with warfarin to prevent stroke in medicare beneficiaries with nonvalvular atrial fibrillation.

BACKGROUND AND
PURPOSE: in controlled trials, anticoagulation with warfarin reduces stroke risk by nearly two thirds, but the benefit has been less pronounced in clinical practice. This report describes the extent of warfarin use, its effectiveness, and its impact on medical costs among Medicare patients with nonvalvular atrial fibrillation.
METHODS: using claims from >2 million beneficiaries in the Centers for Medicare and Medicaid Services 5% Sample Standard Analytic Files, we identified patients with nonvalvular atrial fibrillation from 2004 to 2005. Warfarin use was inferred from 3 or more tests of the international normalized ratio within 1 year. Incidence of ischemic/hemorrhagic stroke and major bleeding was evaluated. Adjusted risk was calculated by Cox proportional-hazards regression. Medical costs (reimbursed amounts in 2006 US dollars) were estimated by multivariate linear regression.
RESULTS: of patients with nonvalvular atrial fibrillation (N=119 764, mean age=79.3 years), 58.5% were categorized as warfarin users based on the study definition. During an average of 2.1 years' follow-up, the rate of ischemic stroke was 3.9 per 100 patient-years. After multivariate adjustment, ischemic stroke incidence was 27% lower in patients taking warfarin than in patients not taking warfarin (P<0.0001), with no increase in hemorrhagic stroke and a slightly elevated risk of a major bleed. Use of warfarin was independently associated with lower total medical costs, averaging $9836 per patient per year.
CONCLUSIONS: these results indicate that 41.5% of Medicare patients with nonvalvular atrial fibrillation are not anticoagulated with warfarin. The incidence of stroke and overall medical costs were significantly lower in patients treated with warfarin.