Usefulness of neutrophil to lymphocyte ratio in patients with chronic obstructive pulmonary disease: a prospective observational study

Background/Aims: Neutrophil to lymphocyte ratio (NLR) in peripheral blood is a useful systemic inflammatory response biomarker. However, NLR has not been studied in patients with chronic obstructive pulmonary disease (COPD). This study was aimed to evaluate the usefulness of NLR in patients with COPD. Methods: NLR was prospectively measured and compared in patients with COPD exacerbation (n = 59), patients with stable COPD (n = 61), and healthy controls (n = 28). NLR in patients with COPD exacerbation was repeatedly measured in the convalescent period. The correlation between NLR and clinical parameters was evaluated, and the predictors for respiratory hospitalization were analyzed by multivariate logistic regression. Results: NLR values were significantly higher in patients with COPD exacerbation compared with stable COPD patients and controls ($12.4{\pm}10.6$, $2.4{\pm}0.7$, $1.4{\pm}0.5$, respectively; p < 0.001). NLR was significantly decreased during the convalescent period in patients with COPD exacerbation ($4.5{\pm}4.6$ vs. $11.5{\pm}8.8$, p < 0.001). NLR exhibited a significant correlation with the body mass index, degree of airway obstruction, dyspnea, and exercise capacity (BODE) index, the 6-minute walk test, and the modified Medical Research Council scale. NLR ${\geq}2.8$ was an independent predictor with a borderline significance for respiratory hospitalization (odds ratio, 2.083; p = 0.079). Body mass index and forced expiratory volume in 1 second were independent predictors for respiratory hospitalization. Conclusions: NLR is a straightforward and effective biomarker of COPD exacerbation that may serve as a predictor for respiratory hospitalization in patients with COPD.