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  • Title: Defining time in therapeutic range for busy clinicians: frequency of dose changes is a good surrogate marker to identify patients with suboptimal anticoagulation with warfarin.
    Author: Vijenthira A, Le Gal G, Castellucci LA, Carrier M.
    Journal: Thromb Res; 2014 Sep; 134(3):584-6. PubMed ID: 25037497.
    Abstract:
    INTRODUCTION: Patients on warfarin with sub-optimal time-in-therapeutic-range (TTR) are more likely to have adverse events. Target-specific oral anticoagulants (TSOACs) are approved and can be used as an alternative to warfarin for a number of indications. Further, the efficacy and safety profiles of the TSOACs compared to warfarin are more favourable when the TTR is ≤65% for certain indications. OBJECTIVE: We aimed to determine simple, sensitive and specific diagnostic tools to identify TTR ≤ 65% during the initial three months of warfarin therapy. METHODS: A cross-sectional study including patients newly initiated on warfarin without any interruption for three months was conducted. TTR was calculated using the Rosendaal method. Patients were stratified by TTR (≤ 65% or >65%). Number of INR measurements, dose changes and INR measurements of ≤ 1.7 or ≥ 4.0 were evaluated as potential diagnostic tools to identify TTR ≤ 65%. RESULTS: 670 patients were included. The most common indication for anticoagulation was venous thromboembolism. The mean TTR in the first three months was 68 ± 21% (Range: 10 to 100%). Three or more dose changes identified TTR ≤ 65% and demonstrated a sensitivity and specificity of 90% (95%CI 86 to 93%) and 56% (95%CI 51 to 61%), respectively. Three or more INR measurements of ≤ 1.7 during the initial three months of anticoagulation showed a sensitivity and specificity of 37% (95%CI 32 to 43%) and 98% (95%CI 96 to 99%), respectively. CONCLUSION: Three or more dose changes and three or more INR measurements of ≤ 1.7 could identify patients with a TTR ≤ 65% in the first three months of warfarin therapy.
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