| Summary: | Abstract 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/μL (IQR 4000-7000cells/μL). Mortality rates among the 34% of patients with elevated BNCs (defined as 6000-15000cells/μL) 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/μL). 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.
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