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KMID : 0869620170340010026
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Journal of Korean Society of Hospital Pharmacists
2017 Volume.34 No. 1 p.26 ~ p.34
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Feasibility of Extending INR Recall Intervals for Patients with Atrial Fibrillation on Warfarin Therapy: A Retrospective Observational Study
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Moon Jeong-Yon
Kim Yu-Ri
Huh Jeong-Won
Cho Eun-Jeong
Kim Hyang-Suk
Cho Yoon-Sook
Han Hyun-Joo
Choi Eue-Keun
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Abstract
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Purpose : Patients on warfarin therapy require frequent testing to achieve therapeutic international normalized ratio (INR) range. However, excessive testing increases the burden and cost. In 2012, ACCP guideline proposed that an INR testing frequency can be done every 12 weeks for stable patients. The aim of our study was to compare the relationship between INR recall intervals after obtaining an in-range (2.0-3.0) INR and anticoagulation control for 6 months, and to evaluate the safety and feasibility of an extended interval.
Methods : From May 2012 to April 2013, we retrospectively reviewed 104 patients with atrial fibrillation at the Seoul National University Hospital, whose warfarin dose had been stable for at least 3 months. Of these, 79 patients (76%) had a single out-of-range INR of ≤0.5 below or above the therapeutic range, and 25 patients (24%) had unexpected INR deviation 0.5, all of whom required a change of the maintenance dose. We compared the INR value, the time in therapeutic range (TTR), and the warfarin dose assessment between INR determinations of ≤5 weeks (short term group, n =30) or 5 weeks (long term group, n=42).
Results : The percentage of time in the therapeutic range was 62.72% in the short term group, compared to 67.29% in the long term group; there was no significant difference between the two groups (p=0.434). No increase in the biologic risk of thromboembolic or hemorrhagic events during 6 months follow-up was observed for the long term group.
Conclusion : Our result suggests that for patients demonstrating a consistent pattern of stable therapeutic INRs, allowing INR recall intervals of up to ≥5 weeks does not result in increased risk for bleeding or thromboembolism. Consideration of a longer interval between INR tests for selected patients may thus be appropriate.
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KEYWORD
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Warfarin, INR monitoring, Time in therapeutic range (TTR), Atrial fibrillation
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