title: Monitoring anticoagulation in atrial fibrillation.
abstract: BACKGROUND
  Randomized control trials and observational studies show high-quality warfarin therapy leads to safe and effective stroke prophylaxis. In usual community practice, patient, physician and health care system factors are barriers to optimal anticoagulation. We examined the predictive relationship between inpatient and outpatient INR values in chronic non-valvular atrial fibrillation (AF) patients hospitalized for ischemic stroke (S), bleed (B) and control events (C) in usual community practice.
  
  
  METHODS
  This nested case-control analysis identified AF patients hospitalized for S, B and C using medical and pharmacy claims spanning 4.5 years ('98-'03) and validating diagnosis with chart abstraction. AF was defined as 2 medical claims for AF >or= 42 days apart with a related prescription claim for warfarin. INRs from both outpatient and inpatient settings were used to yield a continuous history of coagulation status. Time-in-therapeutic-range (TTR) was calculated by Rosendaal's linear interpolation method. Correlation of inpatient and prognostic utility of last outpatient INRs was tested with S or B hospitalizations using univariate and multivariate logistic regression.
  
  
  RESULTS
  Overall, 614 hospitalizations (means: age 73.9, CHADS(2) = 3.24; 52% male) included S (n = 98), B (n = 101) and C (n = 415) events. Average TTR was 28.6% (49.4% at INR <2.0, 21.9% at INR >3.0). First INR on admission (INR <2.0 or >3.0) was associated with S and B hospitalizations (OR-adjusted [95%CI], 1.68 [1.04-2.73] and 1.72 [1.02-2.90]), respectively. Last outpatient INR <2.0 was not associated with S (OR-adjusted [95%CI], 1.12 [0.77-1.81]), and INR >3.0 was not associated with B (OR-adjusted [95%CI], 1.25 [0.67-2.32]). Last outpatient INR measurement occurred at 28, 22 and 24 days (median; S, B & C, respectively) before hospitalization.
  
  
  CONCLUSIONS
  Patients were observed within therapeutic range less than 30% of their time on warfarin. While inpatient INRs were clearly associated with both ischemic stroke and bleed events, last outpatient INR before event was not predictive.
authors.affiliation: HealthCore, 800 Delaware Ave. 5th Floor, Wilmington, DE 19801, USA. csarawate@healthcore.com
authors.forename: Chaitanya
authors.initials: C
authors.lastname: Sarawate
authors.forename: Mirko V
authors.initials: MV
authors.lastname: Sikirica
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Willey
authors.forename: Michael F
authors.initials: MF
authors.lastname: Bullano
authors.forename: Ole
authors.initials: O
authors.lastname: Hauch
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000009:adverse effects / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000097:blood / Q000188:drug therapy*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D014859:Warfarin / Q000009:adverse effects / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014859:Warfarin