Stability of sputum and blood eosinophil levels in COPD

<b>Background:</b> Sputum and blood eosinophil levels predict response to inhaled corticosteroid (ICS) treatment in COPD. We investigated the stability of sputum and blood eosinophils over 6 months in a cohort of highly symptomatic COPD patients. <b>Methods:</b> Sputum and blood differential cell counts (DCC) were obtained at baseline and 6 months (n=48 and 56 respectively). Data were analysed using Spearman Rank’s Test (Prism 8.0, GraphPad, USA) and Intraclass correlation coefficient (ICC) of log-transformed data (SPSS 23.0, IBM, Armonk, USA). Sputum data were normalised via a^†Log(x) or ^‡Log(x+1) transformation to account for zero values (n=38 and 48 respectively). <b>Results:</b> Repeated sputum eosinophil counts showed a correlation between baseline and 6m (rho=0.61, <i>p</i>&lt;0.0001, Fig 1A), with an ICC=0.77^‡ and 0.55^† indicating excellent and good correlations respectively. Blood eosinophils showed excellent correlation with ICC=0.84 (rho=0.70, <i>p</i>&lt;0.0001, Fig 1B). Blood eosinophil levels were correlated with sputum eosinophil % at baseline (rho=0.392, <i>p</i>=0.0013,), and 6 months (rho=0.3328, <i>p</i>=0.0182). <b>Conclusion:</b> Blood eosinophils showed excellent repeatability, while lower (but still good) repeatability for sputum eosinophils were observed. A moderate correlation was observed between these measurements. This research was conducted with support from Astrazeneca UK Limited.