Time in Therapeutic Range for Warfarin — A European Success StoryA Swedish registry and quality-improvement program resulted in a mean TTR of more than 75%.
In studies of warfarin, the average time in therapeutic range (TTR) of international normalized ratio (INR) values has ranged from 56% in retrospective studies to 65% in randomized controlled trials. To improve anticoagulation treatment, the Swedish national quality registry for atrial fibrillation (AF) and anticoagulation was founded in 2006. Participating anticoagulation centers use a Web-based dosing algorithm and are located in both primary care and hospital-based settings. These investigators analyzed registry data from 2008 on 18,391 patients (mean age, 70; 40% women) with 250,142 INR samples at 67 centers (mean time between samples per patient, 23 days; mean samples/patient-year, 13.6). Indications for warfarin included AF (64%), venous thrombosis (19%), and heart valve dysfunction (13%).
In 15,601 patients with a target INR of 2.0, the adjusted mean TTR was 76.2%. With an expanded target INR of 1.8–3.2, the mean TTR increased to 88.4%. Mean TTR was >70% in all age groups, and higher percentages correlated significantly with increasing age. Mean warfarin dose fell with increasing age from 43 mg/week in patients aged 41–50 to 24 mg/week in those aged 81–90 (P<0.001). In an outcomes analysis involving 4273 patients at two centers, the risk for major bleeding was 2.6% per treatment year, and the risk for thrombosis was 1.7% per treatment year overall and 1.4% in patients with AF. Incidence of major bleeding increased significantly with increasing age (P<0.001).
Citation(s):Wieloch M et al. Anticoagulation control in Sweden: Reports of time in therapeutic range, major bleeding, and thrombo-embolic complications from the national quality registry AuriculA. Eur Heart J 2011 Sep 18; 32:2282.
