title: Comparing patient-level and site-level anticoagulation control as predictors of adverse events.
abstract: BACKGROUND
  Percent time in therapeutic range (TTR) is increasingly used to summarize anticoagulation control over time among patients receiving warfarin. Higher TTR improves outcomes of care, but studies have varied regarding whether TTR is best summarized as center-based percent time in therapeutic range (cTTR) or as individual percent time in therapeutic range (iTTR). Our aim was to compare cTTR to iTTR in predicting ischemic stroke, major hemorrhage, and all-cause mortality.
  
  
  METHODS
  Veterans Health Administration data of 57,281 patients receiving warfarin therapy were included. iTTR was calculated using linear interpolation. Each site's mean TTR was calculated, and the cTTR was assigned to all patients at that site. We used Cox proportional hazards to examine cTTR and iTTR as predictors of major hemorrhage, ischemic stroke, and all-cause mortality.
  
  
  RESULTS
  Comparing worst to best quartiles of INR control, cTTR was not a statistically significant predictor of major hemorrhage or ischemic stroke, hazard ratios (HR) were 1.02 (95% confidence interval [CI] 0.93-1.11) and 1.00 (95% CI: 0.88-1.13), respectively. cTTR was a weak predictor of all-cause mortality (HR: 1.14, 95% CI: 1.07-1.22). iTTR predicted major hemorrhage (HR: 1.79, 95% CI: 1.63-1.96), ischemic stroke (HR: 1.91, 95% CI: 1.67-2.19), and all-cause mortality (HR: 2.20, 95% CI: 2.05-2.35).
  
  
  CONCLUSIONS
  iTTR significantly predicted risk of major hemorrhage, ischemic stroke, and all-cause mortality. cTTR was a weak predictor of all-cause mortality. Though cTTR may be a better target for site-level quality improvement efforts, iTTR may be a more suitable measure for use in comparative effectiveness research.
authors: Department of Family Medicine, Boston University School of Medicine, Boston, MA, United States. Electronic address: ramon.cancino@bmc.org.
authors: Ramon S
authors: RS
authors: Cancino
authors: Center for Healthcare Organization and Implementation Research, Bedford VA Medical Center, Bedford, MA, United States; Department of Medicine, Section of General Internal Medicine, Boston University School of Medicine, Boston, MA, United States.
authors: Elaine M
authors: EM
authors: Hylek
authors: Center for Healthcare Organization and Implementation Research, Bedford VA Medical Center, Bedford, MA, United States.
authors: Joel I
authors: JI
authors: Reisman
authors: Center for Healthcare Organization and Implementation Research, Bedford VA Medical Center, Bedford, MA, United States; Department of Medicine, Section of General Internal Medicine, Boston University School of Medicine, Boston, MA, United States.
authors: Adam J
authors: AJ
authors: Rose
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects*; D001777:Blood Coagulation / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D011787:Quality of Health Care; D016896:Treatment Outcome; D014481:United States; D014493:United States Department of Veterans Affairs / Q000706:statistics & numerical data; D014859:Warfarin / Q000008:administration & dosage* / Q000009:adverse effects*
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: Anticoagulants; Health care quality; Hemorrhage; Outcome assessment (health care)