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Original Research: Diffuse Lung Disease |

Idiopathic Pulmonary Fibrosis: Gender-Age-Physiology Index Stage for Predicting Future Lung Function Decline

Margaret L. Salisbury, MD; Meng Xia, MS; Yueren Zhou, MS; Susan Murray, ScD; Nabihah Tayob, ScD; Kevin K. Brown, MD; Athol U. Wells, MD; Shelley L. Schmidt, MD; Fernando J. Martinez, MD; Kevin R. Flaherty, MD
Author and Funding Information

FUNDING/SUPPORT: This study was funded by the National Institutes of Health [Grant K24 HL111316 to Dr Flaherty and Grant T32 HL007749-22].

CORRESPONDENCE TO: Margaret L. Salisbury, MD, 3916 Taubman Center, 1500 E. Medical Center Dr, Ann Arbor, MI 48109-5360


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;149(2):491-498. doi:10.1378/chest.15-0530
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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.

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