title: Developing and validating a risk score for lower-extremity amputation in patients hospitalized for a diabetic foot infection.
abstract: OBJECTIVE
  Diabetic foot infection is the predominant predisposing factor to nontraumatic lower-extremity amputation (LEA), but few studies have investigated which specific risk factors are most associated with LEA. We sought to develop and validate a risk score to aid in the early identification of patients hospitalized for diabetic foot infection who are at highest risk of LEA.
  
  
  METHODS
  Using a large, clinical research database (CareFusion), we identified patients hospitalized at 97 hospitals in the U.S. between 2003 and 2007 for culture-documented diabetic foot infection. Candidate risk factors for LEA included demographic data, clinical presentation, chronic diseases, and recent previous hospitalization. We fit a logistic regression model using 75% of the population and converted the model coefficients to a numeric risk score. We then validated the score using the remaining 25% of patients.
  
  
  RESULTS
  Among 3,018 eligible patients, 21.4% underwent an LEA. The risk factors most highly associated with LEA (P < 0.0001) were surgical site infection, vasculopathy, previous LEA, and a white blood cell count >11,000 per mm(3). The model showed good discrimination (c-statistic 0.76) and excellent calibration (Hosmer-Lemeshow, P = 0.63). The risk score stratified patients into five groups, demonstrating a graded relation to LEA risk (P < 0.0001). The LEA rates (derivation and validation cohorts) were 0% for patients with a score of 0 and ~50% for those with a score of ≥21.
  
  
  CONCLUSIONS
  Using a large, hospitalized population, we developed and validated a risk score that seems to accurately stratify the risk of LEA among patients hospitalized for a diabetic foot infection. This score may help to identify high-risk patients upon admission.
authors.affiliation: Department of Medicine, University of Washington, Seattle, WA, USA. balipsky@uw.edu
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Lipsky
authors.forename: John A
authors.initials: JA
authors.lastname: Weigelt
authors.forename: Xiaowu
authors.initials: X
authors.lastname: Sun
authors.forename: Richard S
authors.initials: RS
authors.lastname: Johannes
authors.forename: Karen G
authors.initials: KG
authors.lastname: Derby
authors.forename: Ying P
authors.initials: YP
authors.lastname: Tabak
mesh_terms: D000368:Aged; D000671:Amputation, Surgical / Q000706:statistics & numerical data*; D017719:Diabetic Foot / Q000601:surgery*; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D016015:Logistic Models; D035002:Lower Extremity / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012307:Risk Factors