Warfarin control in Hong Kong clinical practice

Objectives: Time-in-therapeutic range (TTR) assesses safety and effectiveness of warfarin therapy using international normalized ratio (INR). This study aimed to investigate the status of TTR in Hong Kong and patients’ economic and clinical outcomes. Predictors of poor warfarin control and patient’s knowledge in warfarin therapy were assessed. Methods: A five-month observational study was conducted in Prince of Wales Hospital in Hong Kong. The TTRs calculated using Caucasian and Japanese therapeutic range were examined among patients on warfarin for at least one year. Patients’ knowledge was assessed using the Oral Anticoagulation Knowledge (OAK) test. Results: A total of 259 patients were included in this study, with 174 of them completed the OAK test. Using Caucasian therapeutic range, calculated mean TTR was 40.2 ± 17.1%, compared that of 49.1 ± 16.1% with Japanese therapeutic range (P<0.001). Mean TTR in patients with atrial fibrillation was higher than those with prosthetic heart valve (p<0.001). Predictability of TTR on clinical outcomes and economic outcomes was comparable between Caucasian and Japanese therapeutic range. Patients with ideal TTR had fewer clinical complications and lower warfarin-related healthcare costs. Patients with younger age, concurrent use of aspirin, frusemide, famotidine, pantoprazole and simvastatin were associated with poorer TTR. Mean score of OAK test was 54.1%. Only 24 patients (13.8%) achieved the satisfactory overall score of ≥75% in the test. Conclusion: Warfarin use in Hong Kong patients was poorly controlled regardless of indication. Patients’ knowledge towards warfarin use was suboptimal. More education to patients on warfarin use is warranted.