title: The effect of hospitalization on oral anticoagulation control: a population-based study.
abstract: BACKGROUND
  For patients taking oral anticoagulants (OAC), the proportion of time spent in the therapeutic range is strongly associated with bleeding and thromboembolic risk. Previous studies examining OAC control may not generalize because the patient population was select or INR capture was incomplete.
  
  
  OBJECTIVE
  Measure OAC control for an entire population of elderly people and determine patient factors associated with OAC control.
  
  
  METHODS
  People in Eastern Ontario without valve replacement aged 65 years or greater who were treated with warfarin between 1 September 1999 and 1 September 2000.
  
  
  METHODS
  Retrospective cohort study using population-based administrative databases. OAC control was measured as the proportion of days in therapeutic range (PDTR), defined as the number days with the INR between 2 and 3 divided by total number of days observation. Linear interpolation was used to determine INR levels between measures. Negative binomial regression was used to identify patient factors independently associated with PDTR. We also determined which factors were associated with proportion of days with a critically low (<1.5) or critically high (>/=5) INR.
  
  
  RESULTS
  7179 people were followed for a total of 3238 years. 15% of people were hospitalized during the study. Overall, PDTR was 59.2% (95% CI 59.1%-59.2%). Independent of all other significant factors, hospitalization was associated with a 15% decrease in the PDTR 15% (rate ratio 0.85, 95% CI 0.83-0.87). Hospitalization was also independently associated with greater proportion of time with a critically low INR (rate ratio 1.68, 95% CI 1.51-1.88) and a critically high INR (1.70, 95% CI 1.38-2.08).
  
  
  CONCLUSIONS
  Elderly people in eastern Ontario taking warfarin were therapeutic 59.2% of the time. Independent of other patient factors, patients who are hospitalized have the greatest risk of poor anticoagulation control. Control for anticoagulated patients who get hospitalized should be reviewed to determine if and how it could be improved.
authors.affiliation: Department of Medicine, University of Ottawa, Clinical Epidemiology Program, Ottawa Health Research Institute, C405, Ottawa Hospital, Civic Campus, 1053 Carling Avenue, Ottawa ON, K1Y 4E9, Canada.
authors.forename: Carl
authors.initials: C
authors.lastname: van Walraven
authors.forename: Peter C
authors.initials: PC
authors.lastname: Austin
authors.forename: Natalie
authors.initials: N
authors.lastname: Oake
authors.forename: Philip
authors.initials: P
authors.lastname: Wells
authors.forename: Muhammad
authors.initials: M
authors.lastname: Mamdani
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Forster
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage* / Q000627:therapeutic use; D015331:Cohort Studies; D016208:Databases, Factual; D016903:Drug Monitoring / Q000706:statistics & numerical data; D005260:Female; D006760:Hospitalization; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D012189:Retrospective Studies; D013997:Time Factors; D014859:Warfarin / Q000008:administration & dosage* / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D014859:Warfarin