Adjustment of GAP model for Japanese patients with idiopathic pulmonary fibrosis

Abstract

Background: The GAP (gender, age, and lung physiology) model has been reported to have good predictive and discriminative performances for idiopathic pulmonary fibrosis (IPF) patients with easy calculation. However, we previously reported that in the Japanese IPF cohort, the GAP model did not show accurate model performances like those observed in the original report. We tried adjusting the GAP model using our cohort to show better model performances for Japanese IPF patients. Methods: We included 325 IPF patients in this study. According to the AICc of the Cox proportional hazards regression, we chose gender, age, %VC and %DLCO as prognostic factors, similar to the original GAP model. We trisected values of these factors and made them into points. Moreover, we corrected the weighting of these points based on regression coefficients for each factors. The total points were stratified into Stage I – III, considering the distribution of the number of patients and the survival rate at each stage. Moreover, we validated this ‘adjusted’ model with another IPF cohort (validation cohort) that included 117 patients. Results: Using the adjusted GAP model, the survival rates of each stage were significantly different from each other using the log-rank test. The cumulative mortality rates at each stage a year after diagnosis were 7.0% (Stage I), 26.6% (Stage II) and 40.1% (Stage III), which were close to those of the original report. The model performances were confirmed with the validation cohort. Conclusion: We adjusted the GAP model using the Japanese IPF cohort. By resetting thresholds and points for the GAP parameters, we might adjust the GAP model suitable to respective cohorts.