title: An alternative method of acute lung injury classification for use in observational studies.
abstract: BACKGROUND
  In observational studies using acute lung injury (ALI) as an outcome, a spectrum of lung injury and difficult-to-interpret chest radiographs (CXRs) may hamper efforts to uncover risk factor associations. We assessed the impact of excluding patients with difficult-to-classify or equivocal ALI diagnosis on clinical and genetic risk factor associations for ALI after trauma.
  
  
  METHODS
  This study was of a prospective cohort of 280 critically ill trauma patients. The primary outcome was the development of ALI. Patients were classified into one of three groups: (1) definite ALI (patients who fulfilled the American-European Consensus Conference [AECC] criteria for ALI), (2)equivocal ALI (patients who had difficult-to-interpret CXRs), and (3) definite non-ALI. We compared clinical and genetic ALI risk factor associations between two classification schemes: AECC classification (definite ALI vs rest) and alternative classification (definite ALI vs definite non-ALI, excluding equivocal ALI).
  
  
  RESULTS
  Ninety-three (35%) patients were classified as definite ALI, 67 (25%) as equivocal, and 104 (39%) as definite non-ALI. Estimates of clinical and genetic ALI risk factor associations were farther from the null using the alternative classification. In a multivariable risk factor model, the C statistic of the alternative classification was significantly higher than that derived from the AECC classification (0.82 vs 0.74; P < .01).
  
  
  CONCLUSIONS
  The ability to detect ALI risk factors may be improved by excluding patients with equivocal or difficult-to-classify ALI. Such analyses may provide improved ability to detect clinical and genetic risk factor associations in future epidemiologic studies of ALI.
authors.affiliation: Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University of Pennsylvania School of Medicine, Blockley Hall, 423 Guardian Dr, Philadelphia, PA, USA.
authors.forename: Chirag V
authors.initials: CV
authors.lastname: Shah
authors.forename: Paul N
authors.initials: PN
authors.lastname: Lanken
authors.forename: A Russell
authors.initials: AR
authors.lastname: Localio
authors.forename: Robert
authors.initials: R
authors.lastname: Gallop
authors.forename: Scarlett
authors.initials: S
authors.lastname: Bellamy
authors.forename: Shwu-Fan
authors.initials: SF
authors.lastname: Ma
authors.forename: Carlos
authors.initials: C
authors.lastname: Flores
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Kahn
authors.forename: Barbara
authors.initials: B
authors.lastname: Finkel
authors.forename: Barry D
authors.initials: BD
authors.lastname: Fuchs
authors.forename: Joe G N
authors.initials: JG
authors.lastname: Garcia
authors.forename: Jason D
authors.initials: JD
authors.lastname: Christie
mesh_terms: D055371:Acute Lung Injury / Q000145:classification* / Q000175:diagnosis / Q000209:etiology; D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans; D019370:Observation / Q000379:methods*; D011446:Prospective Studies; D015599:Trauma Severity Indices; D014947:Wounds and Injuries / Q000150:complications*