title: The validity of International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes for identifying patients hospitalized for COPD exacerbations.
abstract: BACKGROUND
  Acute exacerbations of COPD (AE-COPD) are a leading cause of hospitalizations in the United States. To estimate the burden of disease (eg, prevalence and cost), identify opportunities to improve care quality (eg, performance measures), and conduct observational comparative effectiveness research studies, various algorithms based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes have been used to identify patients with COPD. However, the validity of these algorithms remains unclear.
  
  
  METHODS
  We compared the test characteristics (sensitivity, specificity, positive predictive value, and negative predictive value) of four different coding algorithms for identifying patients hospitalized for an exacerbation of COPD with chart review (reference standard) using a stratified probability sample of 200 hospitalizations at two urban academic medical centers. Sampling weights were used when calculating prevalence and test characteristics.
  
  
  RESULTS
  The prevalence of COPD exacerbations (based on the reference standard) was 7.9% of all hospitalizations. The sensitivity of all ICD-9-CM algorithms was very low and varied by algorithm (12%-25%), but the negative predictive value was similarly high across algorithms (93%-94%). The specificity was > 99% for all algorithms, but the positive predictive value varied by algorithm (81%-97%).
  
  
  CONCLUSIONS
  Algorithms based on ICD-9-CM codes will undercount hospitalizations for AE-COPD, and as many as one in five patients identified by these algorithms may be misidentified as having a COPD exacerbation. These findings suggest that relying on ICD-9-CM codes alone to identify patients hospitalized for AE-COPD may be problematic.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Rush University Medical Center, Chicago, IL.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Stein
authors.affiliation: Center for Pharmacoeconomic Research, University of Illinois at Chicago, Chicago, IL.
authors.forename: Adriana
authors.initials: A
authors.lastname: Bautista
authors.affiliation: Center for Pharmacoeconomic Research, University of Illinois at Chicago, Chicago, IL.
authors.forename: Glen T
authors.initials: GT
authors.lastname: Schumock
authors.affiliation: Center for Pharmacoeconomic Research, University of Illinois at Chicago, Chicago, IL; Center for Management of Complex Chronic Care, Hines VA Hospital, University of Chicago, Chicago, IL.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Lee
authors.affiliation: Department of Health Studies, Section of Pulmonary, University of Chicago, Chicago, IL.
authors.forename: Jeffery T
authors.initials: JT
authors.lastname: Charbeneau
authors.affiliation: Department of Health Studies, Section of Pulmonary, University of Chicago, Chicago, IL.
authors.forename: Diane S
authors.initials: DS
authors.lastname: Lauderdale
authors.affiliation: Critical Care Medicine, University of Chicago, Chicago, IL.
authors.forename: Edward T
authors.initials: ET
authors.lastname: Naureckas
authors.affiliation: Section of Hospital Medicine, University of Chicago, Chicago, IL.
authors.forename: David O
authors.initials: DO
authors.lastname: Meltzer
authors.affiliation: Section of Pulmonary, Critical Care, Sleep and Allergy, University of Illinois at Chicago, Chicago, IL. Electronic address: jakris@uic.edu.
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Krishnan
mesh_terms: D000046:Academic Medical Centers / Q000706:statistics & numerical data*; D000368:Aged; D000465:Algorithms; D059019:Clinical Coding / Q000379:methods*; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D038801:International Classification of Diseases; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015995:Prevalence; D029424:Pulmonary Disease, Chronic Obstructive / Q000145:classification* / Q000175:diagnosis / Q000453:epidemiology; D012008:Recurrence; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014481:United States / Q000453:epidemiology