Blood and sputum eosinophilia in chronic obstructive pulmonary disease patients and their association with exacerbations: a prospective observational study from a tertiary care center

Identification of the chronic obstructive pulmonary disease (COPD) phenotype allows selection of the most appropriate drug for each patient. Blood eosinophilia, as a surrogate marker for airway eosinophilia, has been associated with a phenotype of COPD exacerbators. Thus, blood eosinophilia and/or sputum eosinophilia enable healthcare providers to assess disease severity and guide treatment decisions in COPD patients. Understanding these factors can aid in effective COPD management and improve patient outcomes. A prospective observational study was conducted at a tertiary care hospital. A total of 140 diagnosed COPD patients who met the eligibility criteria and attended the Department of Tuberculosis and Respiratory Diseases were included in the study. All recruited patients underwent a thorough clinical assessment, including detailed history taking (with emphasis on exacerbations), physical examination, complete blood count, including absolute eosinophil count (AEC), sputum cytology, and chest X-ray. Eosinophilia was defined as an AEC>150 cells/µL and/or sputum eosinophilia ≥2%. If sputum cytology showed <2% eosinophils and <60% neutrophils, the sample was considered paucicellular, and those patients were excluded from statistical analysis. Appropriate statistical tests were applied to derive inferences. Of the 140 enrolled COPD patients, 83 (59.3%) had stable COPD and 57 (40.7%) were experiencing acute exacerbation. Blood eosinophilia (AEC>150 cells/µL) was present in 76 (54.3%) patients. After excluding sputum samples with paucicellularity (n=69), sputum eosinophilia (≥2%) was present in 41 (57.7%) of the remaining 71 patients. A statistically significant association was observed between blood eosinophilia and a history of exacerbations (p<0.001). Similarly, sputum eosinophilia was significantly associated with a history of COPD exacerbations (p=0.008). COPD severity (GOLD stage) was significantly associated with blood eosinophilia (p=0.044). However, no statistically significant correlation was found between sputum eosinophilia and blood eosinophilia (p=0.5). Measurement of blood and sputum eosinophils facilitates phenotyping of COPD patients and enhances precision in treatment without delay. The use of inhaled corticosteroids targets eosinophilic inflammation in patients with COPD exacerbations. Therefore, we recommend measuring blood eosinophil counts in all patients at the time of COPD diagnosis.