A Simple Ratio in a Complex Disease: Exploring the Neutrophil-to-Lymphocyte Ratio in Idiopathic Pulmonary Fibrosis

The neutrophil-to-lymphocyte ratio (NLR) is a simple, inexpensive and easily accessible inflammatory biomarker that reflects the balance between innate and adaptive immunity. In recent years, NLR has emerged as a potential prognostic and disease severity marker for different diseases, including idiopathic pulmonary fibrosis (IPF), a progressive and fatal interstitial lung disease with a highly variable course and poor prognosis. Several studies have highlighted that NLR can be associated with several clinical outcomes such as lung function decline, increased risk of hospitalization, acute exacerbation of IPF, and mortality over time. It might also correlate with overall survival in the course of antifibrotic therapy and validated prognostic score as a gender–age–physiology score. Despite these findings, the clinical use of NLR remains limited due to its non-specific nature, the lack of standardized cut-off values, and high variability related to demographic factors, comorbidities and medications. Hence, NLR may display the underlying immune dysregulation in IPF and could be exploited as a non-invasive tool for risk stratification and disease monitoring. Further studies are needed to confirm and validate its use in IPF and to establish reliable cut-off values in clinical applications.