Idiopathic Pulmonary Fibrosis (IPF) and Hypersensitivity Pneumonitis (HP): Comparison of GAP, ILD-GAP, CPI Models

<bold>Background:</bold> IPF is a lung disease characterized by progressive fibrosis and a poor prognosis. HP shares similarities with IPF in terms of prognosis in some patients. Various mortality indices have been discussed in the literature to predict the prognosis of IPF. <bold>Objectives:</bold> This study aims to determine the predictive validity of GAP, ILD-GAP, and CPI models in IPF, fibrotic, and non-fibrotic HP patients, evaluate their predictive superiority, and assess the success of predicting mortality. <bold>Methods:</bold> A total of 143 patients were included in this retrospective study; 45 had IPF, 26 had fibrotic HP, and 72 had non-fibrotic HP. GAP index, ILD-GAP index, and CPI score were calculated for each patient using the formula CPI=91-(0.65×DLCO)-(0.53×FVC%)+(0.34×FEV1). <bold>Results:</bold> The mean age was significantly higher in IPF patients compared to other groups. In IPF, GAP (p=0.026; AUC=0.676), ILD-GAP (p=0.026; AUC=0.767) and CPI (p=0.004; AUC=0.726) discriminated mortality and there was no difference in their discrimination power. In non-fibrotic HP, only CPI (p=0.014; AUC=0.666) and in fibrotic HP, GAP (p=0.006; AUC=0.757) and ILD-GAP (p=0.006; AUC=0.757) discriminated mortality. Increased CPI (p=0.002), male gender (p=0.013), ischemic heart disease (p=0.001) and GAP stage I higher than significantly shortened survival time. <bold>Conclusions:</bold> There was no difference between GAP, ILD-GAP, and CPI in predicting prognosis. In IPF; GAP, ILD-GAP, and CPI can all be used. In fibrotic HP, GAP and ILD-GAP can be used, and in non-fibrotic HP, only the CPI can be used. Male gender, the presence of ischemic heart disease, and a high GAP stage were found to be associated with mortality in all groups.