Predictors of Progressive Fibrosing Interstitial Lung Diseases and Survival in Fibrosing Interstitial Lung Disease-Related Usual Interstitial Pneumonia

<i>Background and Objectives:</i> Usual interstitial pneumonia (UIP) is associated with progressive fibrosing interstitial lung diseases (PF-ILD) and poor survival in patients with fibrosing interstitial lung disease (FILD). We aimed to investigate the predictors of PF-ILD and survival in patients with FILD-UIP. <i>Materials and Methods:</i> This retrospective study was conducted at a single, tertiary hospital in China. Patients underwent routine follow-up visits every 3 to 6 months according to standard operating procedures (SOPs). Patients with FILD-UIP were further stratified using the proposed PF-ILD criteria. <i>Results</i>: This retrospective study enrolled 150 patients with FILD-UIP between October 2020 and June 2025, with 117 patients completing follow-up for more than 12 months. FILD-UIP was categorized as idiopathic pulmonary fibrosis (IPF) (<i>n</i> = 67) and non-IPF-UIP (<i>n</i> = 50), which included connective tissue disease-associated UIP (<i>n</i> = 29), hypersensitivity pneumonitis-associated UIP (<i>n</i> = 7), and interstitial pneumonia with autoimmune features-associated UIP (<i>n</i> = 14). During the follow-up period, 32 (47.8%) patients with IPF and 19 (38.0%) non-IPF-UIP experienced PF-ILD. Pulmonary hypertension (PH) and predicted percentage of forced vital capacity (FVC%pred) were dependent risk factors for PF-ILD in patients with FILD-UIP, non-IPF-UIP, and IPF. King's Brief Interstitial Lung Disease (KBILD) is a dependent risk factor for PF-ILD in patients with FILD-UIP and IPF. PF-ILD is similarly associated with poor survival in patients with FILD-UIP, non-IPF-UIP, and IPF. <i>Conclusions</i>: Baseline disease severity is closely associated with the incidence of PF-ILD, with all forms of FILD-UIP at risk of PF-ILD and showing similar outcomes to IPF-UIP/PF-ILD.