Introduction: Time in therapeutic range (TTR) assesses the safety and effectiveness of warfarin therapy using the international normalised ratio. This study investigated the TTR in Hong Kong patients using both European and Japanese therapeutic ranges and patients' economic and clinical outcomes. Predictors of poor warfarin control and patient knowledge concerning warfarin therapy were assessed.
Methods: A 5-month observational study with retrospective and prospective components was conducted in the Prince of Wales Hospital. The study examined electronic patient records of patients who received warfarin for at least 1 year during the period from January 2010 to August 2015. Patient knowledge was assessed via phone interview using the Oral Anticoagulation Knowledge (OAK) test.
Results: In total, 259 patients were included; 174 completed the OAK test. The calculated mean TTR was 40.2±17.1% (European therapeutic range), compared with 49.1±16.1% (Japanese therapeutic range) [P<0.001]. Mean TTR was higher in patients with atrial fibrillation than in patients with prosthetic heart valve (P<0.001). The abilities of TTR to predict clinical and economic outcomes were comparable between European and Japanese therapeutic ranges. Patients with ideal TTR had fewer clinical complications and lower healthcare costs. Patients with younger age exhibited worse TTR, as did those with concurrent use of furosemide, famotidine, or simvastatin. Mean OAK test score was 54.1%. Only 24 (13.8%) patients achieved a satisfactory overall score of ≥75% in the test.
Conclusion: Warfarin use in Hong Kong patients was poorly controlled, regardless of indication. Patient knowledge concerning warfarin use was suboptimal; thus, additional patient education is warranted regarding warfarin.
Keywords: International normalized ratio; Warfarin.