title: Idiopathic Pulmonary Fibrosis: Gender-Age-Physiology Index Stage for Predicting Future Lung Function Decline.
abstract: BACKGROUND
  Idiopathic pulmonary fibrosis is a progressive lung disease with variable course. The Gender-Age-Physiology (GAP) Index and staging system uses clinical variables to stage mortality risk. It is unknown whether clinical staging predicts future decline in pulmonary function. We assessed whether the GAP stage predicts future pulmonary function decline and whether interval pulmonary function change predicts mortality after accounting for stage.
  
  
  METHODS
  Patients with idiopathic pulmonary fibrosis (N = 657) were identified retrospectively at three tertiary referral centers, and baseline GAP stages were assessed. Mixed models were used to describe average trajectories of FVC and diffusing capacity of the lung for carbon monoxide (Dlco). Multivariable Cox proportional hazards models were used to assess whether declines in pulmonary function ≥ 10% in 6 months predict mortality after accounting for GAP stage.
  
  
  RESULTS
  Over a 2-year period, GAP stage was not associated with differences in yearly lung function decline. After accounting for stage, a 10% decrease in FVC or Dlco over 6 months independently predicted death or transplantation (FVC hazard ratio, 1.37; Dlco hazard ratio, 1.30; both, P ≤ .03). Patients with GAP stage 2 with declining pulmonary function experienced a survival profile similar to patients with GAP stage 3, with 1-year event-free survival of 59.3% (95% CI, 49.4-67.8) vs 56.9% (95% CI, 42.2-69.1).
  
  
  CONCLUSIONS
  Baseline GAP stage predicted death or lung transplantation but not the rate of future pulmonary function decline. After accounting for GAP stage, a decline of ≥ 10% over 6 months independently predicted death or lung transplantation.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI. Electronic address: msalisbu@med.umich.edu.
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Salisbury
authors.affiliation: Department of Biostatistics, University of Michigan, Ann Arbor, MI.
authors.forename: Meng
authors.initials: M
authors.lastname: Xia
authors.affiliation: Department of Biostatistics, University of Michigan, Ann Arbor, MI.
authors.forename: Yueren
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Biostatistics, University of Michigan, Ann Arbor, MI.
authors.forename: Susan
authors.initials: S
authors.lastname: Murray
authors.affiliation: Department of Biostatistics, University of Texas MD Anderson Cancer Center, Houston, TX.
authors.forename: Nabihah
authors.initials: N
authors.lastname: Tayob
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, National Jewish Health, Denver, CO.
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Brown
authors.affiliation: Interstitial Lung Disease Unit, Royal Brompton and Harefield National Health Service Foundation Trust, London, England.
authors.forename: Athol U
authors.initials: AU
authors.lastname: Wells
authors.affiliation: Pulmonary Medicine, Spectrum Health, Grand Rapids, MI.
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Schmidt
authors.affiliation: Pulmonary and Critical Care Medicine, Cornell Medical College, New York, NY.
authors.forename: Fernando J
authors.initials: FJ
authors.lastname: Martinez
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Flaherty
mesh_terms: D018450:Disease Progression; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume / Q000502:physiology*; D054990:Idiopathic Pulmonary Fibrosis / Q000150:complications / Q000401:mortality / Q000503:physiopathology*; D011237:Predictive Value of Tests; D011379:Prognosis; D012129:Respiratory Function Tests; D012131:Respiratory Insufficiency / Q000175:diagnosis* / Q000209:etiology / Q000401:mortality; D012189:Retrospective Studies; D012720:Severity of Illness Index; D012737:Sex Factors; D015996:Survival Rate / Q000639:trends; D014481:United States / Q000453:epidemiology
keywords: idiopathic pulmonary fibrosis; interstitial lung disease; lung function