In this issue of CHEST, Bafadhel et al examined the role of blood eosinophil counts (a surrogate marker for airway eosinophilia) as a possible marker for predicting the effect of treatment, including systemic steroids, in patients hospitalized for COPD exacerbations. The authors performed a post hoc analysis of data obtained in a previously performed two-center randomized clinical trial, which examined the effect of early rehabilitation intervention in patients with chronic respiratory disorders hospitalized for acute care. Based on data obtained in patients with a confirmed diagnosis of COPD exacerbation and differential full blood count taken within 12 h of admission, patients were stratified into eosinophilic vs noneosinophilic exacerbations using a cutoff value of ≥ 200 cells/μL and/or 2% blood eosinophils. During hospitalization, 90% of the patients received oral corticosteroids that were almost always administered with antibiotic therapy. The authors reported that 25% of subjects hospitalized for a COPD exacerbation had an eosinophilic exacerbation and that the length of hospital stay was shorter by 1.5 days in these patients, whereas long-term (12 months) follow-up showed no difference between the groups. The authors concluded that acute events requiring hospitalization associated with eosinophilic inflammation may show a rapid response to corticosteroid treatment, hence requiring a shorter length of hospital stay. As in any (good) study, there are limitations to the present analyses. Because almost all of the patients received oral steroids, it remains unclear whether the reduced length of stay was related to a better response to steroids or a better outcome (independent of steroid treatment) in patients with eosinophilic exacerbations. Further, the proposed 25% prevalence of eosinophilic exacerbations will need confirmation because this number could have been affected by exclusion of patients with missing data, timing and dose of oral steroids received before entering in the hospital, the inclusion of patients from only two centers, and the choice of the cutoff values (eg, absolute counts vs percentage). For example, in a recent study examining 647 patients with COPD admitted to the ICU for respiratory failure, the prevalence of patients with blood eosinophils > 2% was < 10%. Another study that was based on a retrospective hospital database analysis found that among 3,084 patients hospitalized for acute exacerbations of COPD, 17% had blood eosinophilia ≥ 300 cells/μL and 40% had blood eosinophilia ≥ 2%. Further studies are clearly required to establish the prevalence of eosinophilic exacerbations in various settings as well as the optimal cutoff values. Interestingly, Bafadhel et al found that eosinophil counts and proportion of eosinophilic exacerbations were markedly lower in patients with consolidation on chest radiographs. Recent data from the European COPD audit suggest that COPD exacerbations with alveolar consolidation are treated in approximately 93% of cases with antibiotics and 79% of cases with systemic steroids. If blood eosinophils are indeed a marker of steroid responsiveness, it is tempting to speculate that overprescription of systemic steroids could be particularly high in this group of patients. Finally, it remains unclear whether high blood eosinophil count is triggered by a stimulus at the time of the exacerbation or whether it represents a stable endotype in patients with COPD. A subgroup of patients with stable COPD appear to have mildly elevated blood eosinophils, a feature that has been suggested to predict the efficacy of fixed combination of inhaled corticosteroids/long-acting β-agonists on reducing the risk of exacerbation. However, there also appears to be some variability in longitudinal eosinophil counts because data from a recent clinical trial indicate that one-half of the patients with a history of sputum eosinophils ≥ 3% within the previous year had blood eosinophils < 200 μL at study entry. Longitudinal follow-up of blood eosinophil counts in patients with eosinophilic exacerbations will provide answers to this important question.