Peripheral blood eosinophil count in COPD: literature data and new findings

Eosinophils play a protective role and are involved in the pathogenesis of exacerbations in chronic obstructive pulmonary disease (COPD). 
The study of the role of eosinophils in pathogenesis of COPD, especially during exacerbations, is relevant to selecting the optimal therapy. The aim was to analyze literature data and compare them with the results of our study in real clinical practice. 
Methods. We analyzed the publications on eosinophil count in COPD in electronic libraries eLIBRARY and National Library of Medicine. In our study, we examined 330 patients, collected their history, and conducted physical examination, spirometry, and laboratory tests. Statistical analysis was carried out using SPSS-18 software.
Results. Analysis of publications showed that percent of patients with COPD with a stable eosinophil count of more than 300 cells/μL varies from 12.3% to 17%. This percentage is variable and can reach 37.5% in patients with exacerbations. As many studies show, eosinophilia is one of the indications for inhaled corticosteroids (ICS) and is associated with better outcomes than eosinopenia. In our study, 18.58% of patients were eligible for ICSs because of their eosinophil count, 53.3% because of > 2 exacerbations, 82.1% because of exacerbations or hospitalizations, and 62.1% because their FEV1  was < 50% of the reference value. Among patients with FEV1  < 50%, 61% had > 2 exacerbations, 87.8% had hospitalizations, and 12.7% had eosinophilia. Only 7.57% of patients with COPD met all three criteria for prescribing ICS. 16.2% of patients had eosinophilia and 2 and more exacerbations within a year. 10.3% of patients had eosinophilia combined with FEV1  less than 50%. 6.7% of patients had eosinophilia, 2 or more exacerbations within a year, and FEV1  < 50%. 
Conclusion. Analysis of literature data and our findings have shown that the eosinophil blood count is one of the important prognostic indicators in COPD. It facilitates selection of the optimal therapy, including triple inhalation therapy.

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