Neutrophil-to-lymphocyte ratio, blood eosinophils and COPD exacerbations: a cohort study

Background Blood neutrophil-to-lymphocyte ratio (NLR) and blood eosinophils (B-Eos) are emerging biomarkers in COPD. This study examined whether they could predict acute exacerbations of COPD (AECOPDs), and determined their longitudinal stability. Methods In this closed cohort study, Swedish subjects with spirometry-verified COPD attended three yearly visits in a stable phase of the disease. Blood cell counts, spirometry and questionnaire-assessed AECOPD-history (worsening of COPD leading to an unscheduled visit and/or use of antibiotics and/or oral corticosteroids) were collected at each visit. Results Of 466 included subjects 57% were female. Baseline meantso forced expiratory volume in 1 s was 58 +/- 17% predicted. High NLR (>= 3.0) was more common in subjects with previous AECOPDs than in those without (33.5% versus 20.4%, p=0.002). In two-level mixed-effects logistic regression models adjusted for confounders, NLR as a continuous variable (OR 1.20, 95% CI 1.04-1.38) and B-Eos >= 300 cells.mu L-1 (OR 1.54, 95% CI 1.06-2.24) were associated with future AECOPDs. In 386 subjects with blood cell data available at all three visits, the intraclass correlation coefficient for NLR was 0.61 (95% CI 0.56-0.66) and for B-Eos 0.69 (95% CI 0.64-0.73). NLR was persistently >= 3.0 in 10.6% and B-Eos was persistently >= 300 cells.mu L-1 in 15.3%. Conclusions Stable phase NLR and B-Eos were associated with future AECOPDs. NLR on its own is probably not useful to predict AECOPDs but might be included in a risk scoring index. A minority of subjects with COPD had persistently elevated stable-phase NLR or B-Eos, and the biomarkers showed fair longitudinal reliability.