Studies have concluded that telephone-based management of warfarin is an effective alternative to in-office management. High rates of patient and physician satisfaction have been reported with telephone-based monitoring. Proposed benefits of telephone-based monitoring include time- and cost savings for patients and healthcare providers alike as well as increased access to care for those patients who have difficulty making in-office appointments. This study aimed to evaluate the impact of telephone versus office-based management of warfarin on extreme INR values. A retrospective cohort study was conducted to assess outcomes of patients receiving warfarin managed either by telephone or in-office appointments. The primary endpoint of the study was the frequency of extreme INR values, defined as an INR ≤1.5 or ≥4.5. A total of 110 patients were evaluated; subjects were distributed 2:1 between the in-office and telephone groups. Baseline characteristics were similar between groups. Subjects followed via telephone had a twofold increase in the incidence of extreme INR values compared to the patients followed in-office (15.18 vs. 7.98 %; p < 0.0001). Overall TTR was similar between groups (85.39 vs. 80.38 %, p = 0.1171). There was no difference between the two groups in the incidence of major bleeding events (2.67 vs. 0 %, p = 1.00), thromboembolic events (8 vs. 0 %, p = 0.1740), or hospitalizations related to anticoagulation therapy (6.67 vs. 0 %, p = 0.1758). Patients monitored via telephone had a higher incidence of extreme INR values than patients followed in-office, which may lead to an increased incidence of adverse outcomes in the long-term. Well-designed, prospective studies are needed to confirm such findings.
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