Can blood eosinophils predict sputum eosinophils in stable COPD?

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Background: In COPD, eosinophilic airway inflammation is associated with disease severity, acute exacerbations and a positive response to systemic corticosteroids. Reliable biomarkers are needed for the detection of eosinophilic COPD. Aim: To investigate whether peripheral blood eosinophil (PBE) count can predict eosinophilic airway inflammation in stable COPD. We hypothesise that there is a positive association between PBE and sputum eosinophilia in COPD patients. Methods: Stable COPD patients (GOLD grade II-IV) with a history of acute exacerbation in the past year underwent spirometry, sputum induction and blood collection. Receiver operating characteristic (ROC) curve analysis was used to examine the predictive relationship between sputum eosinophilia (≥3%) and PBE. Results: 66 patients were recruited, 44 were males, with a mean(±SD) age of 70.51(±7.79) years and post bronchodilator FEV 1 % predicted of 57.04(±18.01)%. Almost half (48.5%) of the patients were 9frequent exacerbators9; 59% were in GOLD quadrant D. Sputum eosinophilia was present in 22 patients (33.3%). A significant correlation was found between sputum eosinophil percentage and PBE counts (r=0.495; p 9 /L). The best cut-off point for PBE count was 0.475×10 9 /L, with a sensitivity of 50%, specificity of 86.36%, and a positive likelihood ratio of 3.7. Conclusion: PBE count has a high specificity for sputum eosinophilia, allowing a positive diagnosis of eosinophilic COPD. This simple test could be used to target inflammation and inform treatment decisions in COPD.