International Normalized Ratio Control in a Warfarin Anticoagulation Clinic: A Cross-Sectional Study

Background: Warfarin is an effective anticoagulant with a narrow therapeutic index. It requires frequent, careful dose adjustment and patient monitoring. This study assesses the International Normalized Ratio (INR) control among patients attending pharmacists-led anticoagulation clinics (ACCs). Methods: An observational cross-sectional study was conducted in ACCs from January to April 2022. INR control was assessed by calculating the proportion of the patient’s time in the therapeutic range (TTR) for the previous three months using the traditional method. The patient’s warfarin knowledge level was assessed using a patient knowledge questionnaire. Spearman correlation analysis investigated the association between questionnaire scores and the demographics. Results: Out of 211 approached patients, 200 patients were included (response rate 94.8%). TTR for all the patients was 68.7%. Out of 200, 113 (56.5%) patients had their INR within therapeutic range. Most patients (n=180, 90%) reported adherence to warfarin. Despite a relatively high mean patient knowledge score (76.1%), one-quarter of patients had poor TTR (TTR < 60%). A weak correlation existed between patients’ knowledge scores and older age (Rs=-0.203, p= 0.004). No significant correlation was observed between patient knowledge scores and other factors (gender or current INR). In multivariable logistic regression, patients having a higher INR showed a 36% increase in the odds of poor TTR (OR = 1.36, 95% CI [ 0.71, 2.61]). Conclusions: Most patients attending ACCs had within normal TTR and acceptable medication knowledge. Older patients had lower knowledge scores. More attention and close monitoring should be given to older patients and those with poor TTR.