The performance of the GAP model in patients with rheumatoid arthritis associated interstitial lung disease

Julie Morisset, Eric Vittinghoff, Bo Young Lee, Roberto Tonelli, Xiaowen Hu, Brett M. Elicker, Jay H. Ryu, Kirk D. Jones, Stefania Cerri, Andreina Manfredi, Marco Sebastiani, Andrew J. Gross, Brett Ley, Paul J. Wolters, Talmadge E. King, Dong Soon Kim, Harold R. Collard, Joyce S. Lee

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Background Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is associated with significant morbidity and mortality. Similarities have been observed between patients with idiopathic pulmonary fibrosis (IPF) and the UIP (usual interstitial pneumonia) form of RA-ILD. The GAP (gender, age, physiology) model has been shown to predict mortality in patients with IPF, but its ability to predict mortality in RA-ILD is not known. Methods We identified 309 patients with RA-ILD at 4 academic centers with ongoing longitudinal cohorts of patients with ILD. The primary endpoint was mortality. To handle missing data (n = 219 subjects with complete dataset), multiple imputation by iterative chained equations was used. Using the GAP model as a baseline, we assessed improvements in mortality risk prediction achieved by incorporating additional variables. Model discrimination was assessed using the c-index, and calibration was checked by comparing observed and expected incidence of death. Results Patients had a mean age of 65 years and were predominantly female (54%). The mean forced vital capacity (FVC) % predicted was 73 and the mean diffusing capacity for carbon monoxide (DLCO) % predicted was 55. Twenty-four percent of the 236 patients with a high-resolution computed tomography scan available for review had a definite UIP pattern. The original GAP model, including gender, age, FVC%, and DLCO%, had a c-index of 0.746 in our cohort. Calibration of this model was satisfactory at 1, 2 and 3 years. Model discrimination was not meaningfully improved by adding other clinical variables. Conclusion The GAP model that was derived for IPF performs similarly as a mortality risk prediction tool in RA-ILD.

Original languageEnglish (US)
Pages (from-to)51-56
Number of pages6
JournalRespiratory Medicine
StatePublished - Jun 1 2017


  • Interstitial lung disease
  • Prognosis
  • Rheumatoid arthritis
  • Risk assessment

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine


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