Association Between Neutrophil-Lymphocyte Ratio and All-Cause Mortality in Critically Ill Patients with Chronic Obstructive Pulmonary Disease: A Retrospective Cohort Study.

BACKGROUND Neutrophil-lymphocyte ratio (NLR) is related to increased mortality risk in many diseases. However, there is limited research on critically ill patients with chronic obstructive pulmonary disease (COPD). A retrospective cohort study was performed to investigate whether NLR can be used as a biomarker to predict the mortality of critically ill COPD patients. MATERIAL AND METHODS In the research, the data were gathered from the database of the Medical Information Mart for Intensive Care-IV. The 28-day mortality was defined as the primary outcome, while the secondary outcomes were in-hospital and 90-day mortality. Through the application of the Kaplan-Meier curves and the multivariate Cox regression analysis, the potential association between NLR and mortality for critically ill patients with COPD was evaluated. For subgroup analysis, age, sex, ethnicity, mean blood pressure, and comorbidities were considered. RESULTS We extracted data on 2650 patients, of which 53.7% were male. A higher level of NLR was correlated with higher 28-day mortality risk. Compared to the lower quartile (NLR<4.56), HR (95% CI) of the upper quartile (NLR>16.86) was 1.75 (1.21-2.52) in the multivariate Cox regression model when adjusted for confounders (P=0.003). A similar tendency was found in the 90-day mortality (HR=1.59, 95% CI=1.16-2.19, P=0.004) and the in-hospital mortality (HR=1.71, 95% CI=1.22-2.42, P=0.002). Subgroup analyses showed that the correlation between NLR and 28-day mortality was stable. CONCLUSIONS The higher level of NLR is likely to be correlated with the increase of the all-cause mortality risk in critically ill patients with COPD, but this needs to be validated in future prospective research.