Original Research: Diffuse Lung Disease |

Predicting Survival Across Chronic Interstitial Lung DiseasePredicting Survival in Interstitial Lung Disease: The ILD-GAP Model

Christopher J. Ryerson, MD; Eric Vittinghoff, PhD; Brett Ley, MD; Joyce S. Lee, MD; Joshua J. Mooney, MD; Kirk D. Jones, MD; Brett M. Elicker, MD; Paul J. Wolters, MD; Laura L. Koth, MD; Talmadge E. King, Jr, MD, FCCP; Harold R. Collard, MD, FCCP
Author and Funding Information

From the Department of Medicine (Dr Ryerson), University of British Columbia, Vancouver, BC, Canada; the Department of Biostatistics (Dr Vittinghoff), the Department of Medicine (Drs Ley, Lee, Wolters, Koth, King, and Collard), the Department of Radiology (Dr Jones), and the Department of Pathology (Dr Elicker), University of California, San Francisco, San Francisco, CA; and the Department of Medicine (Dr Mooney), Stanford University, Stanford, CA.

Correspondence to: Christopher J. Ryerson, MD, St. Paul’s Hospital, 1081 Burrard St, Ward 8B, Vancouver, BC, V6Z 1Y6, Canada; e-mail: chris.ryerson@hli.ubc.ca

For editorial comment see page 672

Funding/Support: Funding was provided by the Nina Ireland Lung Disease Program.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.

Chest. 2014;145(4):723-728. doi:10.1378/chest.13-1474
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Background:  Risk prediction is challenging in chronic interstitial lung disease (ILD) because of heterogeneity in disease-specific and patient-specific variables. Our objective was to determine whether mortality is accurately predicted in patients with chronic ILD using the GAP model, a clinical prediction model based on sex, age, and lung physiology, that was previously validated in patients with idiopathic pulmonary fibrosis.

Methods:  Patients with idiopathic pulmonary fibrosis (n = 307), chronic hypersensitivity pneumonitis (n = 206), connective tissue disease-associated ILD (n = 281), idiopathic nonspecific interstitial pneumonia (n = 45), or unclassifiable ILD (n = 173) were selected from an ongoing database (N = 1,012). Performance of the previously validated GAP model was compared with novel prediction models in each ILD subtype and the combined cohort. Patients with follow-up pulmonary function data were used for longitudinal model validation.

Results:  The GAP model had good performance in all ILD subtypes (c-index, 74.6 in the combined cohort), which was maintained at all stages of disease severity and during follow-up evaluation. The GAP model had similar performance compared with alternative prediction models. A modified ILD-GAP Index was developed for application across all ILD subtypes to provide disease-specific survival estimates using a single risk prediction model. This was done by adding a disease subtype variable that accounted for better adjusted survival in connective tissue disease-associated ILD, chronic hypersensitivity pneumonitis, and idiopathic nonspecific interstitial pneumonia.

Conclusion:  The GAP model accurately predicts risk of death in chronic ILD. The ILD-GAP model accurately predicts mortality in major chronic ILD subtypes and at all stages of disease.

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