Combined assessment of the GAP index and body mass index at antifibrotic therapy initiation for prognosis of idiopathic pulmonary fibrosis

Antifibrotic therapy (AFT) slows disease progression in patients with idiopathic pulmonary fibrosis (IPF). The Gender-Age-Physiology (GAP) index, was developed based on data at IPF diagnosis before the introduction of AFT and has not been evaluated in the AFT context. Further, recent advances have revealed the importance of body-composition factors in prognosis of IPF treated with AFT. This multi-centre, retrospective study aimed to evaluate the GAP index and body mass index (BMI) at the time of AFT initiation for predicting prognosis in patients with IPF. This study included two patient cohorts of IPF receiving AFT, Hamamatsu cohort (n = 110) and Seirei cohort (n = 119). The distribution of GAP stages I, II, and III was 38.2%, 43.6%, and 18.2%, respectively, in Hamamatsu cohort; in Seirei cohort, it was 41.2%, 50.4%, and 8.4%, respectively. In both cohorts, the GAP index distinctly classified prognosis into three groups (log-rank test). Interestingly, a lower BMI showed prognostic value independent of the GAP index in multivariate analyses. Subsequently, combining the GAP index with BMI at AFT initiation successfully divided the patients with IPF into four distinct prognoses. Assessment of the GAP index and BMI measurement at AFT initiation are important for predicting prognosis in patients with IPF.