Peripheral blood eosinophilia predicts lower airway eosinophilia in asthma and COPD

Background: New treatments for asthma & COPD may require evaluation in sub-groups with lower airway eosinophilia or neutrophilia. A non-invasive test to identify these phenotypes may reduce unnecessary sputum induction at screening. Aim: To establish whether eosinophil and neutrophil counts correlate with those in the lower airway in asthma and COPD patients. Methods: 35 patients with ICS-treated asthma and 44 patients with COPD underwent sputum induction and phlebotomy on ≤ 3 occasions over 1 yr. Differential white cell counts were performed on peripheral blood and induced sputum; Spearman9s test was used to assess a correlation. Results: 97 paired samples from 35 asthma patients; 111 paired samples from 44 COPD patients were analysed. Proportion of eosinophils in peripheral blood correlated positively with proportion of eosinophils in induced sputum in asthma (r =0.61, 95% CI 0.47 to 0.73, P 3% was 74% in asthma and 42% in COPD; specificity was 84% in both asthma and COPD; positive predictive value was 78% in asthma and 56% in COPD; and negative predictive value was 81% in asthma and 75% in COPD. There was no correlation between proportion of neutrophils in peripheral blood vs. induced sputum (for asthma, r =-0.18, 95% CI 0.37 to 0.03, P=0.08; for COPD, r=0.15, 95% CI -0.05 to 0.33, P=0.13). Conclusions: Eosinophil counts in induced sputum were positively correlated with those in peripheral blood in patients with asthma and COPD. A peripheral blood eosinophilia screening test could be used to identify patients with lower airway eosinophilia.