title: Burden of potentially avoidable anticoagulant-associated hemorrhagic and thromboembolic events in the elderly.
abstract: BACKGROUND
  On average, patients receiving therapy with oral anticoagulants (OACs) in the community are in the therapeutic range only 55% of the time. Anticoagulation control strongly influences the risk of hemorrhagic and thromboembolic events in such patients. However, not all anticoagulation-associated events are attributable to poor anticoagulation control, nor do all hemorrhagic or thromboembolic events occur in anticoagulated patients.
  
  
  OBJECTIVE
  Measure the proportion of serious hemorrhagic and thromboembolic events that would be avoided if anticoagulation control was perfect.
  
  
  METHODS
  A retrospective cohort study of eastern Ontario using population-based administrative databases. Anticoagulation control was determined for each day of OAC exposure using linear interpolation. Incident hemorrhagic or thromboembolic hospitalizations for control and OAC patients were identified. Hemorrhages and thromboemboli in OAC patients were deemed to be avoidable if they occurred at international normalized ratios of > 3 and < 2, respectively.
  
  
  RESULTS
  The study included > 183,000 patient-years of observation with 6,400 patient-years of OAC exposure. Anticoagulation control could be determined for 51.5% of OAC exposure time. Control patients had hemorrhagic and thromboembolic event rates of 1.8% and 1.5% per year, respectively. A total of 10,020 people were exposed to OACs, and spent 14.2% and 26.7% of the time, respectively, with excessively high and low anticoagulation intensity. Excessively high anticoagulation intensity explained 25.6% (95% confidence interval [CI], 19.4 to 31.7) and 2.0% (95% CI, 1.5 to 2.5) , respectively, of all serious hemorrhages in the anticoagulated and entire population. Excessively low anticoagulation intensity explained 11.1% (95% CI, 4.4 to 17.7) and 1.1% (95% CI, 0.7 to 1.6) of all thromboemboli, respectively.
  
  
  CONCLUSIONS
  Our study showed that extreme anticoagulation intensity significantly impacted the health of the population. Improving anticoagulation control will have significant effects on the incidence of serious hemorrhagic and thromboembolic events in the both the anticoagulated and entire populations.
authors.affiliation: Clinical Epidemiology Program, Ottawa Health Research Institute, Ottawa Hospital, Civic Campus, 1053 Carling Avenue, Ottawa, Ontario, Canada. carlv@ohri.ca
authors.forename: Carl
authors.initials: C
authors.lastname: van Walraven
authors.forename: Natalie
authors.initials: N
authors.lastname: Oake
authors.forename: Philip S
authors.initials: PS
authors.lastname: Wells
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Forster
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use*; D015331:Cohort Studies; D016001:Confidence Intervals; D017281:Cost of Illness; D004305:Dose-Response Relationship, Drug; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced* / Q000453:epidemiology / Q000517:prevention & control*; D006801:Humans; D015994:Incidence; D019934:International Normalized Ratio; D008297:Male; D009864:Ontario / Q000453:epidemiology; D012189:Retrospective Studies; D018570:Risk Assessment; D013923:Thromboembolism / Q000453:epidemiology / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants