Different impacts of blood and sputum eosinophil counts on lung function and clinical outcomes in asthma: findings from the COREA cohort

Abstract Purpose Blood (EOS-B) and sputum (EOS-S) eosinophil counts may contribute differently to asthma pathogenesis. We compared the impact of the baseline EOS-B and EOS-S levels on lung function, asthma control, and exacerbation in Korean asthma patients. Methods Asthma patients with baseline EOS-B (n=4257) and EOS-S (n=1049) levels from a multicenter cohort (COREA) were included. Pulmonary function test (%FEV1 predicted), asthma control test (ACT), and asthma exacerbation incidence were followed-up every 3 months for one year. Linear mixed effect models and survival analyses were used to examine the association between eosinophilic groups defined by EOS-B or EOS-S and outcomes. Results High eosinophilic groups were associated with a low baseline value and a high improvement in the %FEV1 predicted and ACT scores over time. The magnitude of group difference in %FEV1 predicted was 2-fold higher in the EOS-S versus EOS-B classification (mean and 95% CI: 4.7 (0.6-8.8) versus 2.0 (0.2-3.7) for the baseline value and -1.5 (-2.3 to -0.8) versus -0.8(-1.1 to -0.4) for the slope of change), whereas it was identical in ACT score. The magnitude of the impact increased linearly with the elevation of the cut-off level for the EOS-B but remained stable for the EOS-S classification. Patients with an elevation of both their EOS-B and EOS-S showed a higher increment in the %FEV1 predicted and ACT over time. Neither the EOS-B nor EOS-S was associated with asthma exacerbation. Conclusion EOS-S and EOS-B contribute differently to the clinical outcomes and should be taken into account independently to improve asthma care.