Time in Therapeutic Range and Outcomes After Warfarin Initiation in Newly Diagnosed Atrial Fibrillation Patients With Renal Dysfunction

Background It is unknown whether renal dysfunction conveys poor anticoagulation control in warfarin‐treated patients with atrial fibrillation and whether poor anticoagulation control associates with the risk of adverse outcomes in these patients. Methods and Results This was an observational study from the Stockholm CREatinine Measurements (SCREAM) cohort including all newly diagnosed atrial fibrillation patients initiating treatment with warfarin (n=7738) in Stockholm, Sweden, between 2006 and 2011. Estimated glomerular filtration rate (eGFR; mL/min per 1.73 m 2 ) was calculated from serum creatinine. Time‐in‐therapeutic range (TTR) was assessed from international normalized ratio (INR) measurements up to warfarin cessation, adverse event, or end of follow‐up (2 years). Adverse events considered a composite of intracranial hemorrhage, ischemic stroke, myocardial infarction, or death. During median 254 days, TTR was 83%, based on median 21 INR measurements per patient. TTR was 70% among patients with eGFR P =0.2). Conclusion Severe chronic kidney disease (eGFR 75%) is associated with lower risk of adverse events, independently of underlying renal function.