Evaluating time in therapeutic range for hemodialysis patients taking warfarin

Warfarin is frequently used in the hemodialysis (HD) population for atrial fibrillation (AF) and venous thromboembolism (VTE); however, there is insufficient evidence to support this practice. Given that HD patients have 3 - 10 times the risk for both stroke and bleeding than the general population, anticoagulation in these patients is controversial. Time in therapeutic range (TTR) is accepted as a surrogate outcome of clinical effectiveness and safety of warfarin. The primary objective of this study was to evaluate TTR in an HD population. A 6-year retrospective chart review was performed in 46 HD patients on warfarin (target international normaized ratio (INR)=2-3). One year of patient data was collected, which included weekly INRs, demographics and clinical outcomes. TTR was calculated using the Rosendaal and fraction of INRs in range methods. The mean TTR using the Rosendaal and fraction of INRs in range method was 49.2±14.6% and 44.2±13.5%, respectively. Patients were 3 times more likely to be below target than above it, suggesting they were more often at risk of inadequate efficacy rather than toxicity. There were 9 serious bleeding and 9 thrombotic events; these occurred in patients with a TTR<60%. For the 9 serious bleeding events, the median INR on the day of the event was 2.1 (IQR 1.81-2.75). In conclusion, this HD unit is not meeting the TTR goal established in the literature and patients are often subtherapeutic. Further studies to investigate ways to improve TTR are warranted. Ultimately, a prospective study evaluating the safety and efficacy of warfarin in HD patients is needed.