Background. It is believed that high blood eosinophils are important indicators of poor prognosis and increased exacerbations in COPD. However, variability and long term role of these cells in COPD is not known.
Aim Long term investigation of the variability and the possible role of blood eosinophils in clinical outcomes of smokers with and without COPD.
Methods 512 smokers (303 with and 209 without COPD) were followed for at least 5 years with annual examination, blood eosinophils and lung function. Subjects were categorized according to blood eosinophils in all 5 visits as persistently high (≥150 cells/µL), persistently low (<150 cells/µL), or variable (< and >150 cells/µL).
Results Distribution of blood eosinophils was similar in smokers with and without COPD (median/range: 160; 0-2125 vs 156; 0-1190 cells/µL). Considering all 5 visits, 18% of smokers with COPD had eosinophils persistently high, 17% persistently low, and 65% variable. Smokers without COPD showed a similar pattern. No difference was found among COPD subjects with high, low and variable eosinophils in: bronchodilator response (mean±SD: 9±12 vs 10±11 vs 8±11%), FEV1 decline (23±44 vs 32±63 vs 32±51 ml/year) and disease severity. The number of medically diagnosed exacerbations/year was similar in the three eosinophil groups (0.96±2 vs 1.2±2 vs 0.99±2). In COPD subjects a high number of eosinophils was associated with reduced mortality (Kaplan-Meier p=0.001).
Conclusions There is a large yearly variability in eosinophils number in COPD. Persistently high eosinophils are not related to worst clinical outcome and might be beneficial. Therefore the use of blood eosinophils as a biomarker of bad prognosis is likely to be a premature hypothesis.