Peripheral Blood Eosinophils as Marker of Sputum Eosinophilia and Outcome of COPD Exacerbation
Sputum eosinophils might predict response to inhaled corticosteroids (ICS) in patients with advanced chronic obstructive pulmonary disease (COPD). Induction of sputum requires expertise and may not always be successful. Aim was to investigate correlation and predictive relationship between peripheral blood eosinophils (bEo) and sputum eosinophils (sEo), and impact of peripheral blood eosinophilia on outcome of COPD exacerbation. 120 current smokers with COPD (GOLD group C) (57.4 ± 0.92 years, M/F ratio 1.4), with no blood (≥7% or >0.43x109/L) nor sputum (≥3%) eosinophilia, were treated with moderate dose of ICS and long-acting bronchodilatator during stable disease, but systemic corticosteroids and antibiotics during exacerbation. According to sputum eosinophilia (≥4%) during exacerbation, patients were divided into eosinophilic (n=45) and non-eosinophilic group (n=75). In stable disease, bEo and sEo were similar in both groups (p>0.05). During exacerbation, bEo and sEo were significantly higher in eosinophilic group (eosinophilic vs. non-eosinophilic: blood: 1.42 ± 0.39 x109/l vs. 0.23 ± 0.02 x109/l, p<0.001; sputum: 8% (4, 19) vs. 1% (0, 3), p<0.0001), but bEo correlated with sEo in both groups (eosinophilic: r=0.52, p<0.001; non-eosinophilic: r=0.25, p<0.05). Relative bEo predicted sputum eosinophilia (area under the curve=0.71, standard error=0.05; 95% confidence interval [CI] =0.61-0.81; p<0.001) and enabled identification of the presence or absence of sputum eosinophilia in 82% of the cases at a threshold of ≥4% (specificity=83.56%, sensitivity=93.83%, positive likelihood ratio=3.67). Eosinophilic group during exacerbation showed less frequent hospitalisations and shorter exacerbation (eosinophilic vs. non-eosinophilic: hospitalisations: 26.7% vs. 60.0%, p<0.001; duration of exacerbation (days): 8.1±0.35 vs. 10.13±0.31, p<0.0001). In COPD exacerbation, relative peripheral blood eosinophils ≥4% might identify sputum eosinophilia. Blood eosinophilia indicate better outcome of COPD exacerbation. Further investigations are needed to predict eosinophilic exacerbation in COPD patients, with prior absence of sputum or blood eosinophilia.