Predictors of International Normalized Ratio Variability in Patients With Atrial Fibrillation Under Warfarin Therapy.

Background: Variability in the international normalized ratio (INR) of prothrombin time has been suggested to be related to outcome in patients with atrial fibrillation (AF) under warfarin therapy, but its determinants remain unclear.
Methods and results: The study population consisted of 626 AF patients under warfarin therapy in the Shinken Database (n=22,230). INR variability was calculated by Fihn's method. Determinants of high log INR variability (defined as over mean+standard deviation) were determined by logistic regression analyses. Symptomatic heart failure (odds ratio [OR] 3.974, 95% confidence interval [CI] 2.510-6.292), older age (≥75 years old; OR 2.984, 95% CI 1.844-4.826) and severe renal dysfunction (eGFR <30 mL/min/1.73 m ² ; OR 3.918, 95% CI 1.742-8.813) were identified as independent predictors of high INR variability on multivariate logistic regression analysis.
Conclusions: The determinants of INR variability in AF patients under warfarin therapy could assist Japanese clinicians in identifying patients likely to show unstable warfarin control irrespective of the definition of the target INR range.