title: Validation of length of hospital stay as a surrogate measure for injury severity and resource use among injury survivors.
abstract: OBJECTIVE
  While hospital length of stay (LOS) has been used as a surrogate injury outcome when more detailed outcomes are unavailable, it has not been validated. This project sought to validate LOS as a proxy measure of injury severity and resource use in heterogeneous injury populations.
  
  
  METHODS
  This observational study used four retrospective cohorts: patients presenting to 339 California emergency departments (EDs) with a primary International Classification of Diseases, Ninth Revision (ICD-9), injury diagnosis (years 2005-2006); California hospital injury admissions (a subset of the ED population); trauma patients presenting to 48 Oregon EDs (years 1998-2003); and injured Medicare patients admitted to 171 Oregon and Washington hospitals (years 2001-2002). In-hospital deaths were excluded, as they represent adverse outcomes regardless of LOS. Duration of hospital stay was defined as the number of days from ED admission to hospital discharge. The primary composite outcome (dichotomous) was serious injury (Injury Severity Score [ISS] >or= 16 or ICD-9 ISS <or= 0.90) or resource use (major surgery, blood transfusion, or prolonged ventilation). The discriminatory accuracy of LOS for identifying the composite outcome was evaluated using receiver operating characteristic (ROC) analysis. Analyses were also stratified by age (0-14, 15-64, and >or=65 years), hospital type, and hospital annual admission volume.
  
  
  RESULTS
  The four cohorts included 3,989,409 California ED injury visits (including admissions), 236,639 California injury admissions, 23,817 Oregon trauma patients, and 30,804 Medicare injury admissions. Composite outcome rates for the four cohorts were 2.1%, 29%, 27%, and 22%, respectively. Areas under the ROC curves for overall LOS were 0.88 (California ED), 0.74 (California admissions), 0.82 (Oregon trauma patients), and 0.68 (Medicare patients). In general, the discriminatory value of LOS was highest among children, tertiary trauma centers, and higher volume hospitals, although this finding differed by the injury population and outcome assessed.
  
  
  CONCLUSIONS
  Hospital LOS may be a reasonable proxy for serious injury and resource use among injury survivors when more detailed outcomes are unavailable, although the discriminatory value differs by age and the injury population being studied.
authors.affiliation: Center for Policy and Research in Emergency Medicine, Department of Emergency Medicine, Oregon Health & Science University, Portland, OR, USA. newgardc@ohsu.edu
authors.forename: Craig D
authors.initials: CD
authors.lastname: Newgard
authors.forename: Ross
authors.initials: R
authors.lastname: Fleischman
authors.forename: Esther
authors.initials: E
authors.lastname: Choo
authors.forename: O John
authors.initials: OJ
authors.lastname: Ma
authors.forename: Jerris R
authors.initials: JR
authors.lastname: Hedges
authors.forename: K John
authors.initials: KJ
authors.lastname: McConnell
mesh_terms: D000007:Abdominal Injuries / Q000453:epidemiology; D000293:Adolescent; D000328:Adult; D000368:Aged; D002140:California; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D015601:Injury Severity Score; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D009922:Oregon; D017063:Outcome Assessment, Health Care; D012372:ROC Curve; D012189:Retrospective Studies; D013124:Spinal Injuries / Q000453:epidemiology; D013898:Thoracic Injuries / Q000453:epidemiology; D015599:Trauma Severity Indices; D014947:Wounds and Injuries / Q000453:epidemiology*; D055815:Young Adult