title: A new risk scheme to predict warfarin-associated hemorrhage: The ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) Study.
abstract: OBJECTIVE
  The purpose of this study was to develop a risk stratification score to predict warfarin-associated hemorrhage.
  
  
  BACKGROUND
  Optimal decision making regarding warfarin use for atrial fibrillation requires estimation of hemorrhage risk.
  
  
  METHODS
  We followed up 9,186 patients with atrial fibrillation contributing 32,888 person-years of follow-up on warfarin, obtaining data from clinical databases and validating hemorrhage events using medical record review. We used Cox regression models to develop a hemorrhage risk stratification score, selecting candidate variables using bootstrapping approaches. The final model was internally validated by split-sample testing and compared with 6 published hemorrhage risk schemes.
  
  
  RESULTS
  We observed 461 first major hemorrhages during follow-up (1.4% annually). Five independent variables were included in the final model and weighted by regression coefficients: anemia (3 points), severe renal disease (e.g., glomerular filtration rate <30 ml/min or dialysis-dependent, 3 points), age ≥75 years (2 points), prior bleeding (1 point), and hypertension (1 point). Major hemorrhage rates ranged from 0.4% (0 points) to 17.3% per year (10 points). Collapsed into a 3-category risk score, major hemorrhage rates were 0.8% for low risk (0 to 3 points), 2.6% for intermediate risk (4 points), and 5.8% for high risk (5 to 10 points). The c-index for the continuous risk score was 0.74 and 0.69 for the 3-category score, higher than in the other risk schemes. There was net reclassification improvement versus all 6 comparators (from 27% to 56%).
  
  
  CONCLUSIONS
  A simple 5-variable risk score was effective in quantifying the risk of warfarin-associated hemorrhage in a large community-based cohort of patients with atrial fibrillation.
authors.affiliation: Department of Medicine, University of California, San Francisco, San Francisco, California, USA. mfang@medicine.ucsf.edu
authors.forename: Margaret C
authors.initials: MC
authors.lastname: Fang
authors.forename: Alan S
authors.initials: AS
authors.lastname: Go
authors.forename: Yuchiao
authors.initials: Y
authors.lastname: Chang
authors.forename: Leila H
authors.initials: LH
authors.lastname: Borowsky
authors.forename: Niela K
authors.initials: NK
authors.lastname: Pomernacki
authors.forename: Natalia
authors.initials: N
authors.lastname: Udaltsova
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Singer
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000188:drug therapy; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced*; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome; D014859:Warfarin / Q000009:adverse effects* / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D014859:Warfarin