Association of Neutrophil-to-Lymphocyte Ratio and Systemic Immune Inflammation Index with Inflammatory Burden in Interstitial Lung Diseases

Introduction: Interstitial Lung Diseases (ILDs) involve chronic inflammation and fibrosis. Neutrophil-to-Lymphocyte Ratio (NLR) and Systemic Immune-inflammation Index (SII) are potential systemic inflammation markers. This retrospective case-control study evaluated NLR and SII in Idiopathic Pulmonary Fibrosis (IPF) and Connective-Tissue-Disease-associated ILD (CTDILD). Methods: Medical records from a Bengaluru tertiary-care centre were reviewed (November 2022– November 2023). 120 ILD patients (60 IPF, 60 CTD-ILD) were compared with 120 healthy controls. Patients with COPD, asthma, infections, malignancies, or haematological disorders were excluded. NLR and SII were calculated from routine blood counts at diagnosis. ANOVA was used for statistical analysis (p < 0.05). Results: Both markers were significantly elevated in ILD patients versus controls. Mean NLR: IPF 6.38 ± 2.1, CTD-ILD 4.53 ± 1.8, controls 1.93 ± 0.9 (p < 0.0001). Mean SII: IPF 1,425.2 ± 510.4, CTD-ILD 1,417.7 ± 478.6, controls 551.4 ± 210.3 (p < 0.0001). No significant difference existed between IPF and CTD-ILD groups (p > 0.05). Discussion: Elevated NLR and SII reflect heightened systemic inflammation in ILD, supporting their utility as accessible biomarkers. Similar values between IPF and CTD-ILD suggest limited discriminatory power for subtyping but validate their role in assessing inflammatory burden. Conclusion: NLR and SII are significantly elevated in ILD patients, validating their clinical utility as markers of inflammation. Further prospective studies should establish prognostic value and optimal integration into clinical assessment.