The goal of this retrospective observational study is to evaluate and compare the prognostic value of GAP, ILD-GAP, and CPI scoring systems in patients diagnosed with interstitial lung diseases (ILDs), specifically Idiopathic Pulmonary Fibrosis (IPF), fibrotic Hypersensitivity Pneumonitis, and non-fibrotic Hypersensitivity Pneumonitis.

The main questions it aims to answer are:

• Can GAP, ILD-GAP, and CPI scores accurately predict prognosis in IPF, fibrotic HP, and non-fibrotic HP patients?
• Are there differences in prognostic performance of these models across different ILD subtypes?

Researchers will compare the prognostic utility of GAP, ILD-GAP, and CPI scores between IPF, fibrotic HP, and non-fibrotic HP groups to see if one scoring system offers superior predictive power.

Participants:

• Adults aged ≥18 years
• Diagnosed between October 2011 and October 2021 at the University of Health Sciences Yedikule Chest Diseases and Thoracic Surgery Training and Research Hospital
• 143 patients in total (IPF: 45, fibrotic HP: 26, non-fibrotic HP: 72)

Participants' data will include:

• Clinical and demographic characteristics
• Symptom duration
• Radiologic imaging findings
• Pulmonary function test (PFT) results
• Bronchoalveolar lavage (BAL) findings
• Histopathological diagnoses

Scoring systems will be calculated using standardized formulas as follows:

• GAP (Gender, Age, Physiology)
• ILD-GAP (modified GAP for CTD-ILDs)
• CPI (Composite Physiologic Index = 91 - [0.65 × %DLCO] - [0.53 × %FVC] + [0.34 × %FEV1])

This is a retrospective observational study designed to evaluate and compare the prognostic performance of three widely used scoring systems-Gender-Age-Physiology (GAP) Index, Interstitial Lung Disease-GAP (ILD-GAP) Index, and Composite Physiologic Index (CPI)-in patients diagnosed with interstitial lung diseases (ILDs). The study focuses specifically on three ILD subtypes: Idiopathic Pulmonary Fibrosis (IPF), fibrotic Hypersensitivity Pneumonitis (HP), and non-fibrotic HP.

The primary objective is to determine whether GAP, ILD-GAP, and CPI scores can accurately predict overall survival across these patient groups. A secondary aim is to compare the prognostic performance of the scoring systems to explore whether one model provides superior predictive value in specific ILD subtypes.

The study cohort includes adult patients (≥18 years) who were diagnosed between October 2011 and October 2021 at the University of Health Sciences Yedikule Chest Diseases and Thoracic Surgery Training and Research Hospital. A total of 143 patients were identified and included: 45 patients with IPF, 26 with fibrotic HP, and 72 with non-fibrotic HP.

Data collected for each patient include clinical and demographic characteristics, duration of symptoms, high-resolution computed tomography (HRCT) findings, pulmonary function test (PFT) results, bronchoalveolar lavage (BAL) findings, and histopathological diagnoses where available. The final diagnosis in each case was established through multidisciplinary team (MDT) discussions and/or histopathological confirmation.

The scoring systems were calculated using standardized formulas:

GAP Index: based on gender, age, and physiology (FVC % predicted, DLCO % predicted).

ILD-GAP Index: a modification of the GAP model for use in connective tissue disease-associated and other ILDs.

CPI (Composite Physiologic Index): calculated as 91 - (0.65 × %DLCO) - (0.53 × %FVC) + (0.34 × %FEV1).

By applying these validated prognostic models to a real-world ILD cohort, the study aims to provide insights into their relative accuracy, clinical utility, and potential limitations. Findings are expected to contribute to more precise prognostic assessment and risk stratification in patients with fibrotic and non-fibrotic ILDs.

Inclusion Criteria:

• 40 patients diagnosed with IPF based on clinical features, laboratory findings, thoracic HRCT results, and/or histopathological confirmation, as determined by a multidisciplinary team discussion.
• 40 patients diagnosed with Fibrotic Hypersensitivity Pneumonitis based on clinical features, laboratory findings, and thoracic HRCT results, confirmed in a multidisciplinary team discussion.
• 40 patients diagnosed with Non-Fibrotic Hypersensitivity Pneumonitis based on clinical features, laboratory findings, and thoracic HRCT results, confirmed in a multidisciplinary team discussion.
• Male and female patients over 18 years of age.

Exclusion Criteria:

• Patients under 18 years of age

Patients diagnosed with Chronic Hypersensitivity Pneumonitis (fibrotic/non-fibrotic) and Idiopathic Pulmonary Fibrosis (IPF) by multidisciplinary discussion between October 2011 and October 2021 at the University of Health Sciences Yedikule Chest Diseases and Thoracic Surgery Training and Research Hospital.