Stability of Neutrophil to Lymphocyte Ratio in Acute Exacerbation of Chronic Obstructive Pulmonary Disease and Its Relationship with Clinical Outcomes: A Retrospective Cohort Study.

Background: More studies have focused on the clinical value of the measurement of the neutrophil-to-lymphocyte ratio (NLR) in acute exacerbations of chronic obstructive pulmonary disease (AECOPD). This study aims to assess the stability of NLR in hospitalized AECOPD patients and its relationship with clinical prognosis. Methods: This retrospective observational study recruited patients hospitalized with AECOPD from January 2020 to December 2023. Using receiver operating characteristic curves, we determined the optimal NLR cutoff, categorizing NLR stability into four groups: persistent high (NLR ≥ 3.8), increased (NLR < 3.8 at admission but ≥ 3.8 at discharge), decreased (NLR ≥ 3.8 at admission but < 3.8 at discharge), and persistent low (NLR < 3.8). Adverse hospital outcomes included hospital mortality, transfer to the intensive care unit (ICU), invasive mechanical ventilation (IMV), and length of hospital stay (LOS) ≥ 14 days. The associations between NLR stability and these outcomes were analyzed using multivariable logistic regression and Cox hazard analysis. Results: Among 841 patients hospitalized for AECOPD, the mean age was 72.1±9.5 years, with 644 males (76.6%) and 197 females (23.4%). The proportions and distribution for groups: persistent high, decreased, increased, and persistent low groups were 109 (12.9%), 175 (20.8%), 216 (25.7%), and 341 (40.5%), respectively. The persistent high group had the worst outcomes, including higher IMV use, ICU transfer, LOS > 14 days, and hospital cost, compared to the persistent low group. Compared to the persistent high group, the persistent low group (HR: 0.13; 95% CI: 0.10-0.24) and the decreased group (HR: 0.40; 95% CI: 0.22-0.73) are statistically significant for the risk of death, while the increased group (HR: 0.63; 95% CI: 0.37-1.04) does not show a statistically significant difference. Conclusion: AECOPD patients who have persistent low NLR group face a low risk of adverse hospital outcomes and mortality after 6 months after discharge. The stability of NLR may serve as a novel biomarker for identifying AECOPD patients at increased risk of poor hospital outcomes.