A simple method to identify patients on long-term warfarin who may derive the most benefit from new oral anticoagulants

Abstract

In many countries, new oral anticoagulants are only covered for patients with suboptimal anticoagulation control on vitamin K antagonists (VKAs). The quality of VKA management is often reported using the time in therapeutic range (TTR). We sought to predict a TTR 65% or less using a surrogate measure [number of changes in VKA dose and number of international normalized ratio (INR) tests] that could be easily determined by primary care physicians. This cross-sectional study included consecutive patients whose VKA therapy was managed in a specialized anticoagulation clinic. Patients were dichotomized according to their TTR in the past 6 months (TTR > or ≤ 65%). The ability of the number of INR tests and VKA dose changes to predict TTR group was assessed using receiver-operating characteristics (ROC) curve analysis. The analyses included 1381 patients with a median age of 63 years. The mean TTR was 81% (interquartile range 70-90) and 17.4% of patients had a TTR 65% or more. Based on the ROC curve, patients were stratified according to whether they had either 3 or more dose changes or 9 or more INR tests within the last 6 months. The sensitivity to identify patients with TTR 65% or less was 87% and the specificity was 63%. The number of dose changes and the number of INR tests might be used as indicators of TTR; they could offer a simple way for clinicians to identify patients who are good candidates for the new oral anticoagulants. However, external validation studies in different clinical settings are needed to confirm these findings.

Dedicated warfarin care programme results in superior warfarin control in Queensland, Australia

“…This is similar to findings by Singer et al who correlated TTRs of around 66% to an average INR testing frequency of 19‐21 days. In contrast, Carrier et al associated poor control (TTR<65%) with a median of 12 tests over a six‐month period or a testing interval of 15 days. In addition, Schaefer et al identified poor control to be associated with long intervals between measurements but defined this as >14 days.…”

“…Tight control of INR between 2.0 and 3.0 is the strategy used to ensure optimal benefit of warfarin while minimising risk . Time in therapeutic range (TTR) is a routinely used measure of warfarin control in clinical settings, with patients obtaining lower TTR more likely to experience negative outcomes such as haemorrhage or stroke . A minimum threshold TTR of 65% is recommended, but wide variations of TTR have been demonstrated by different countries and clinical settings …”

Quality of warfarin control in atrial fibrillation patients in South East Queensland, Australia

“…Poor control of TTR <65% was suggested by Carrier et al 29 to be associated with a median of 12 tests over a 6-month period (equating to a testing interval of 15 days). In contrast, we report lower mean TTR with increased frequency of testing; in particular, a frequency of less than 7 days was associated with a TTR of 63.7%.…”

“…Poor control of TTR <65% was suggested by Carrier et al . to be associated with a median of 12 tests over a 6‐month period (equating to a testing interval of 15 days).…”

Factors influencing warfarin control in Australia and Singapore

“…The testing interval of 17 days in Australia and 29 days in Singapore was similar to results from Oh et al(30) who reported a median interval of testing of 14 days in other world regions compared to 28 days in Asia. Carrier et al(31) concluded that patients with 9 or more INR tests and 3 or more dose changes in a six month period were more likely to have a TTR<65%. In contrast, our Australian population with an average of 10 tests and a mean 2.5 dose changes in the six month study had a high TTR of 82%.…”