Association Between Elevated Neutrophil-to-Lymphocyte Ratio and Mortality Risk in Community-Acquired Pneumonia: A Systematic Review and Meta-Analysis.

The neutrophil-to-lymphocyte ratio (NLR), derived from routine complete blood count parameters, has emerged as a potential prognostic biomarker reflecting systemic inflammation and immune dysfunction. This systematic review and meta-analysis evaluated the association between elevated NLR and mortality risk in community-acquired pneumonia (CAP) patients. A comprehensive literature search was conducted across multiple databases from January 2011 to August 2025, identifying studies that measured NLR in adult CAP patients with mortality as an endpoint. Twelve observational studies were included, comprising diverse patient populations across different healthcare settings. Random-effects meta-analysis was performed using R software (R Foundation for Statistical Computing, Vienna, Austria), with relative risk as the primary effect measure. Quality assessment was conducted using the Newcastle-Ottawa Scale. The pooled analysis demonstrated that elevated NLR was significantly associated with increased all-cause mortality risk in CAP patients (RR: 2.02, 95% CI: 1.18-3.47, p<0.05). Patients with high NLR values had approximately twice the risk of death compared to those with lower ratios. Pooled analysis showed that high NLR was associated with increased risk of ICU admission (RR: 1.30, 95% CI: 1.11-1.53). Substantial heterogeneity was observed across studies (I² = 99% for mortality, 85% for ICU admission), likely reflecting variations in patient populations, NLR cutoff values, and clinical settings. Sensitivity analysis confirmed the robustness of findings. This meta-analysis supports NLR as a valuable, cost-effective prognostic biomarker for mortality prediction in CAP patients, potentially enhancing clinical decision-making when integrated with existing severity assessment tools.