Longitudinal measurements of blood eosinophils in relation to COPD outcomes

Background: Better characterisation of inflammation is advocated in COPD. High blood eosinophils (B-Eos) have been reported to relate with poorer outcome. There is scarce data on this relation in broader COPD populations as well as on changes in B-Eos over time. Aim: To study B-Eos and changes in B-Eos over 1 year with regard to COPD outcomes in the Swedish Tools for Identifying Exacerbations (TIE)-study. Methods: A total of 388 subjects (57% women) with available data on B-Eos at baseline visit and at 1-year follow-up were included. Questionnaire-based data on exacerbations (use of antibiotics and/or oral steroids due to COPD worsening) and lung function data were available at both visits. Results: B-Eos levels (median (IQR)) were similar at both visits: 200 cells/mm3 (100, 300). The proportion of subjects with high B-Eos (≥300 cells/mm3) was similar at baseline (27%) and follow-up (29%), p=0.19. Comparing subjects with high baseline B-Eos to those with normal B-Eos, the proportion reporting ≥1 exacerbation during the following year was similar: 28% vs 29%, p=0.85. FEV1 deteriorated to a lesser extent in subjects with high B-Eos: median change -5 mL vs -40 mL, p=0.02. Among subjects with high baseline B-Eos, 74 (72%) had persistent high levels at 1 year. Comparing subjects with persistent high B-Eos to those with normal B-Eos at both visits, exacerbation rate was similar (26% vs 30%, p=0.48) whereas FEV1 deteriorated to a lesser extent (median change 20 ml vs -30 ml, p=0.009). Conclusions: In the TIE-study, B-Eos levels in COPD patients varied to a limited degree over 1-year. Neither elevated baseline B-Eos nor persistently elevated B-Eos related to exacerbations. However, elevated B-Eos related to less FEV1 decline.