Blood neutrophil counts are associated with exacerbation frequency and mortality in COPD

Background Identifying patients with COPD at increased risk of poor outcomes is challenging due to disease heterogeneity. Potential biomarkers need to be readily available in real-life clinical practice. Blood eosinophil counts are widely studied but few studies have examined the prognostic value of blood neutrophil counts (BNC). Methods In a large population-based COPD registry in the East of Scotland (TARDIS: Tayside Allergic and Respiratory Disease Information System), BNC were compared to measures of disease severity and mortality for up to 15 years follow-up. Potential mechanisms of disease modification by BNC were explored in a nested microbiome substudy. Results 178,120 neutrophil counts were obtained from 7220 people (mean follow up 9 years) during stable disease periods. Median BNC was 5200cells/mu L (IQR 4000-7000cells/mu L). Mortality rates among the 34% of patients with elevated BNCs (defined as 6000-15000cells/mu L) at the study start were 80% higher (14.0/100 person years v 7.8/100py,P < 0.001) than those with BNC in the normal range (2000-6000cells/mu L). People with elevated BNC were more likely to be classified as GOLD D (46% v 33%P < 0.001), have more exacerbations (mean 2.3 v 1.3/year, P < 0.001), and were more likely to have severe exacerbations (13% vs. 5%, P < 0.001) in the following year. Eosinophil counts were much less predictive of these outcomes. In a sub-cohort (N = 276), patients with elevated BNC had increased relative abundance of Proteobacteria and reduced microbiome diversity. Conclusion High BNC may provide a useful indicator of risk of exacerbations and mortality in COPD patients.