Performance of GAP and ILD-GAP models in predicting lung transplant or death in interstitial pneumonia with autoimmune features.

Objectives: To assess the ability of two risk prediction models in interstitial lung disease (ILD) to predict death or lung transplantation in a cohort of patients with interstitial pneumonia with autoimmune features (IPAF).

Methods: We performed a retrospective cohort study of adults with IPAF at an academic medical centre. The primary outcome was a composite of lung transplantation or death. We applied the patient data to the previously described Gender-Age-Physiology (GAP) and ILD-GAP models to determine the ability of these models to predict the composite outcome. Model discrimination was assessed using the c-index, and model calibration was determined by comparing the incidence ratios of observed vs expected deaths.

Results: Ninety-four patients with IPAF were included. Mean (s.d.) age was 58 (13.5) years and the majority were female (62%). The majority met serologic and morphologic criteria for IPAF (94% and 91%, respectively). The GAP model had a c-index of 0.664 (95% CI 0.547-0.781), while the ILD-GAP model had a c-index of 0.569 (95% CI 0.440-0.697). In those with GAP stage 1 or GAP stage 2 disease, calibration of the GAP model was satisfactory at 2 and 3 years for the cumulative end point of lung transplantation or death.

Conclusion: In patients with IPAF, the GAP model performed well as a predictor of lung transplantation or death at 2 years and 3 years from ILD diagnosis in patients with GAP stage 1 and GAP stage 2 disease.