title: Comparison of international normalized ratio audit parameters in patients enrolled in GARFIELD-AF and treated with vitamin K antagonists.
abstract: Vitamin K antagonist (VKA) therapy for stroke prevention in atrial fibrillation (AF) requires monitoring of the international normalized ratio (INR). We evaluated the agreement between two INR audit parameters, frequency in range (FIR) and proportion of time in the therapeutic range (TTR), using data from a global population of patients with newly diagnosed non-valvular AF, the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF). Among 17 168 patients with 1-year follow-up data available at the time of the analysis, 8445 received VKA therapy (±antiplatelet therapy) at enrolment, and of these patients, 5066 with ≥3 INR readings and for whom both FIR and TTR could be calculated were included in the analysis. In total, 70 905 INRs were analysed. At the patient level, TTR showed higher values than FIR (mean, 56·0% vs 49·8%; median, 59·7% vs 50·0%). Although patient-level FIR and TTR values were highly correlated (Pearson correlation coefficient [95% confidence interval; CI], 0·860 [0·852-0·867]), estimates from individuals showed widespread disagreement and variability (Lin's concordance coefficient [95% CI], 0·829 [0·821-0·837]). The difference between FIR and TTR explained 17·4% of the total variability of measurements. These results suggest that FIR and TTR are not equivalent and cannot be used interchangeably.
authors.affiliation: Primary Care Clinical Sciences, School of Health and Population Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK.
authors.forename: David A
authors.initials: DA
authors.lastname: Fitzmaurice
authors.affiliation: Thrombosis Research Institute, London, UK.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Accetta
authors.affiliation: Formerly Technical University of Munich, Munich, Germany.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Haas
authors.affiliation: Thrombosis Research Institute, London, UK.
authors.forename: Gloria
authors.initials: G
authors.lastname: Kayani
authors.affiliation: School of Medicine, National University of Tucumán, San Miguel de Tucumán, Argentina.
authors.forename: Hector
authors.initials: H
authors.lastname: Lucas Luciardi
authors.affiliation: Global Clinical Development, Bayer HealthCare Pharmaceuticals, Berlin, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Misselwitz
authors.affiliation: Duke Clinical Research Institute, Durham, NC, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Pieper
authors.affiliation: Laboratory for Clinical Thrombosis and Hemostasis, Department of Internal Medicine, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Hugo
authors.initials: H
authors.lastname: Ten Cate
authors.affiliation: Department of Medicine, McMaster University Hamilton, Canada.
authors.forename: Alexander G G
authors.initials: AG
authors.lastname: Turpie
authors.affiliation: Thrombosis Research Institute, London, UK.|Department of Surgery, University College London, London, UK.
authors.forename: Ajay K
authors.initials: AK
authors.lastname: Kakkar
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000150:complications*; D020000:Decision Support Systems, Clinical; D005260:Female; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods*; D008297:Male; D008875:Middle Aged; D020521:Stroke / Q000517:prevention & control*; D014812:Vitamin K / Q000037:antagonists & inhibitors*; D014859:Warfarin / Q000627:therapeutic use
chemical_list: D014812:Vitamin K; D014859:Warfarin
keywords: atrial fibrillation; frequency in range; international normalized ratio; time in therapeutic range; vitamin K antagonists