• Abirami Vijenthira, Gregoire Le Gal, Lana A Castellucci, and Marc Carrier.
• Department of Medicine, The Ottawa Hospital Research Institute at the University of Ottawa, Ontario, Canada.
• Thromb. Res. 2014 Sep 1; 134 (3): 584-6.

IntroductionPatients 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.ObjectiveWe aimed to determine simple, sensitive and specific diagnostic tools to identify TTR ≤ 65% during the initial three months of warfarin therapy.MethodsA 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%.Results670 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.ConclusionThree 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.Copyright © 2014 Elsevier Ltd. All rights reserved.

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