Validation of the GAP score in Korean patients with idiopathic pulmonary fibrosis

Abstract

Background: No study has determined whether the risk of mortality predicted by the GAP (gender, age, and physiologic variables) model matches the observed mortality from idiopathic pulmonary fibrosis (IPF) in non-Western populations. We evaluated the clinical course of IPF and validated the GAP model in Korean patients with IPF.

Methods: We included 268 patients who received a diagnosis of IPF at Seoul National University Hospital between 2005 and 2009. For each patient, demographics and clinical data, such as lung physiologic parameters at IPF diagnosis, were evaluated. We validated the GAP model using discrimination and calibration to predict the risk of death in Korean patients with IPF.

Results: The study population comprised 181 men and 87 women (mean age, 65.9 years). The mean baseline % predicted FVC was 77, and % predicted diffusing capacity of lung for carbon monoxide was 65.9. A total of 157 deaths (58.6%) occurred during follow-up, and the median time to death was 4.64 years. The observed cumulative mortality at 1, 2, and 3 years was 10.4%, 20.9%, and 31.0%, respectively. The GAP model produced estimates of 1-year mortality risk consistent with the observed data (C statistic: GAP calculator, 0.74; GAP index and staging system, 0.72; P < .29). However, calibration of the GAP model at 3 years was not satisfactory.

Conclusions: The GAP model showed similar discrimination power compared with the original cohort but did not predict the 3-year risk of death accurately. Further multinational validation studies are needed.