*Article* **Is Blood Eosinophil Count a Biomarker for Chronic Obstructive Pulmonary Disease in a Real-World Clinical Setting? Predictive Property and Longitudinal Stability in Japanese Patients**

**Koichi Nishimura 1,\*, Masaaki Kusunose 1, Ryo Sanda 1, Mio Mori 1, Ayumi Shibayama <sup>2</sup> and Kazuhito Nakayasu <sup>3</sup>**


**Abstract:** The authors examined predictive properties and the longitudinal stability of blood eosinophil count (BEC) or three strata (<100 cells/mm3, 100–299 cells/mm3 and <sup>≥</sup>300 cells/mm3) in patients with chronic obstructive pulmonary disease (COPD) for up to six and a half years as part of a hospitalbased cohort study. Of the 135 patients enrolled, 21 (15.6%) were confirmed to have died during the follow-up period. Episodes of acute exacerbation of COPD (AECOPD) were identified in 74 out of 130 available patients (56.9%), and admission due to AECOPD in 35 out of 132 (26.5%). Univariate Cox proportional hazards analyses revealed that almost all the age, forced expiratory volume in 1 s (FEV1) and health status measures using St. George's Respiratory Questionnaire (SGRQ) Total and COPD Assessment Test (CAT) Score were significantly related to these types of events, but the relationship between age and AECOPD did not reach statistical significance (*p* = 0.05). Neither BEC nor the three different groups stratified by BEC were significant predictors of any subsequent events. There were no significant differences in the BEC between Visits 1–3 (*p* = 0.127, Friedman test). The ICC value was 0.755 using log-transformed data, indicating excellent repeatability. In the case of assigning to strata, Fleiss' kappa was calculated to be 0.464, indicating moderate agreement. The predictive properties of BEC may be limited in a real-world Japanese clinical setting. Attention must be paid to the fact that the longitudinal stability of the three strata is regarded as moderate.

**Keywords:** inhaled corticosteroids (ICS); chronic obstructive pulmonary disease (COPD); blood eosinophil count (BEC); eosinophil; the Global Initiative for Chronic Obstructive Lung Disease (GOLD); acute exacerbation of COPD (AECOPD)
