The neutrophil-to-lymphocyte ratio as a marker of chronic obstructive pulmonary disease and its exacerbations: A systematic review and meta-analysis

Introduction: The main white blood cell populations, neutrophils and lymphocytes, are involved in the pathophysiology of chronic obstructive pulmonary disease (COPD). We conducted a systematic review and meta-analysis of studies investigating the relationship between the neutrophil to lymphocyte ratio (NLR, a marker of subclinical inflammation), presence of COPD, and its exacerbations. Methods: A comprehensive literature search was conducted in Pubmed, Web of Science and Scopus databases; two investigators independently reviewed suitable studies. Results: Nine studies, from 247 initially identified, were included in the meta-analysis. Seven studies, in 775 COPD patients with stable disease and 496 healthy controls, showed a significant increase in NLR values in stable COPD (standardised mean difference, SMD, 0.773, 95% CI 0.410-1.136; P < 0.001). Furthermore, in six studies in 527 COPD patients with acute exacerbation and 620 COPD patients with stable disease, NLR values were significantly higher in patients with exacerbations (random effects SMD 0.850, 95% CI 0.549-1.151; P < 0.001). Conclusions: Our meta-analysis showed that NLR values are significantly higher in stable COPD patients when compared to healthy individuals, although the magnitude of the difference is reduced after trim and fill adjustment, and in patients with COPD exacerbations when compared to patients with stable disease. Further studies, in larger cohorts, are needed to confirm whether the NLR is a useful tool in discriminating between COPD patients with stable disease, those with acute exacerbations, and subjects without the disease.