COPD is a common respiratory condition characterised by persistent airflow limitation and frequent exacerbations. In patients with COPD exacerbations, the optimal route for administering steroid therapy—whether by inhalation or systemically—remains unclear. To address this, we aimed to evaluate the response of sputum and blood eosinophil counts to systemic and inhaled steroids in hospitalised patients with COPD exacerbation. In patients receiving intravenous steroid treatment, all values decreased compared to baseline; however, only the percentage of eosinophils in the sputum showed a statistically significant decrease on the 14th and 45th days of treatment. Systemic steroid treatment significantly decreased the percentage of sputum eosinophils.
Although up to 40% of patients with COPD exhibit eosinophilic airway inflammation and systemic eosinophilia, the role of eosinophils in COPD pathophysiology remains inadequately understood. High sputum and blood eosinophil levels in patients with stable COPD are considered markers of high mortality and increased risk of frequent exacerbations. Epidemiological studies have demonstrated that circulating eosinophils significantly impact COPD outcomes [13]. In two extensive studies with over 30 years of follow-up, eosinophilia (blood eosinophils >275 cells/μL) increased the risk of all-cause mortality independent of age, sex, smoking, and lung function [14]. Another epidemiological study (Copenhagen General Population Study) reported an increased risk of all exacerbations, regardless of severity, with over two-fold increase in the risk of severe exacerbations at blood eosinophil levels >340 cells/μL [14].
Eosinophils may increase airway biopsies and sputum during COPD exacerbations [15]. In COPD exacerbations, blood eosinophil counts can help predict the clinical course, risk of rehospitalisation, length of hospitalisation, response to steroids, and mortality risk. A blood eosinophil count ≥2% increases the risk of all-cause rehospitalisation by 2.3 times and the risk of COPD-related rehospitalisation by 3.5 times [16]. Additionally, the blood eosinophil count is reportedly an independent predictor of mortality in COPD exacerbation [17]. A blood eosinophil count <50 cells/μL during the exacerbation period has been associated with prolonged hospitalisation and a threefold increase in mortality risk [17].
Sputum eosinophilia has long been recognised as a biomarker of the clinical benefit of systemic steroid therapy in patients with stable COPD [18], showing improvements in lung function, symptom reduction, and increased exercise capacity. A treatment approach targeting the reduction of sputum eosinophil counts with systemic steroid therapy has been shown to be beneficial in reducing symptoms and severe COPD exacerbations that require hospitalisation [19]. Patients with high sputum eosinophil counts showed decreased sputum eosinophil levels and significantly improved quality-of-life scores post-systemic steroid treatment [20]. Similar studies have shown that patients with high sputum eosinophil counts responded favourably to systemic steroid treatment [21]. These results highlight the efficacy of eosinophil-targeted systemic steroids in patients with COPD with an eosinophilic phenotype, suggesting that measuring the sputum eosinophil counts may help identify patients with COPD who have steroid-sensitive disease and guide treatment decisions.
Similar to systemic steroid therapy, inhaled steroid therapy in patients with stable COPD and eosinophilic inflammation improves lung function, reduces exacerbations, and lowers sputum eosinophil counts [22]. In a study, patients with stable COPD and elevated blood eosinophil counts had reduced exacerbation rates when treated with inhaled steroids [23]. Brightling et al. demonstrated that in patients with stable COPD and sputum eosinophilia, high-dose inhaled mometasone treatment improved lung function without affecting sputum eosinophilia [18]. A meta-analysis suggested that inhaled steroid treatment may reduce sputum eosinophil counts in patients with stable COPD [24]. Barnes et al. reported that an inhaled salmeterol/fluticasone propionate combination reduced sputum eosinophil counts in patients with stable COPD [25].
Unfortunately, we did not have data on the sputum and blood eosinophil levels of our patients in the stable period, preventing us from comparing these levels with those during exacerbation. We were also unable to compare the eosinophil levels on days 14 and 45 post-exacerbation with the pre-exacerbation eosinophil levels, limiting our ability to assess the treatment’s effects on eosinophils during the stable period.
Eosinophilic COPD exacerbations respond more rapidly to systemic steroid therapy than non-eosinophilic exacerbations, and treatment success is higher [4]. A similar finding was reported in a study comparing the prednisolone and placebo effects on eosinophilic exacerbations [26]. Treatment failure was significantly lower in the systemic steroid group compared to the placebo group (11% and 66%, respectively). However, there is no consensus on the optimal threshold for circulating eosinophil counts to guide systemic steroid therapy. A blood eosinophil value ≥2% during exacerbation is generally considered beneficial for oral steroid therapy [27].
Elevated sputum and blood eosinophil levels are considered good biomarkers for a favourable clinical response to steroid treatment during exacerbation, as well as in stable patients [28]. Current guidelines recommend short-term systemic steroid therapy for all severe COPD exacerbations, regardless of the eosinophilic phenotype [1]. However, for a more individualised treatment approach, systemic steroid treatment may be considered a more rational approach only for exacerbations with high blood eosinophil counts. The use of high-dose nebulised steroids has been suggested as an alternative to systemic steroid therapy for treating exacerbations [29]. In this case, high doses of nebulised steroids can be used for non-eosinophilic COPD exacerbations to achieve optimal clinical outcomes and avoid the side effects of systemic steroids. Günen et al. compared the efficacy of nebulised bronchodilator therapy with that of intravenous steroid therapy in 159 patients with COPD hospitalised for exacerbation [29]. Patients were divided into three groups: standard bronchodilator therapy, intravenous steroids (40 mg/day prednisolone), and nebulised budesonide (1,500 mcg twice daily) for 10 days. Arterial blood gas and pulmonary function test results improved rapidly in the second and third groups. No significant difference was observed in efficacy between patients receiving nebulised budesonide and those receiving intravenous steroid treatment. A similar study was conducted by Mirici et al. [30].
Forty patients with COPD hospitalised for moderate-to-severe exacerbations received nebulised budesonide (8 mg/day) or intravenous prednisolone (40 mg/day). The improvements in arterial blood gases and pulmonary function test results were comparable between the groups. These two studies indicated that high-dose nebulised steroid therapy could be a viable alternative to systemic steroid therapy in patients hospitalised for COPD exacerbation. Good clinical responses can be obtained with inhaled steroid therapy in patients with exacerbated COPD and high eosinophil counts in the blood and sputum. However, no significant decrease in the blood eosinophil count was observed in patients receiving inhaled steroid therapy for COPD exacerbation [31].
Bathoorn showed that inhaled steroid and beta-2 agonist combination therapy reduced sputum eosinophil counts during COPD exacerbation [32]. In their study, 45 patients with COPD exacerbation were treated with budesonide/formoterol (320/9 mcg four times daily), prednisolone (30 mg/day), or placebo for 14 days as outpatients. The primary endpoint of this study was to determine the efficacy on sputum eosinophil levels. Budesonide/formoterol (-57%) and prednisolone (-58%) significantly reduced sputum eosinophil counts compared to the placebo (+24%) (p = 0.01). Significant improvement in symptoms was also observed in steroid-treated patients.
In the FLAME (Effect of Indacaterol Glycopyrronium and Fluticasone/Salmeterol in COPD Exacerbations) study, inhaled steroid use in patients with stable COPD did not reduce blood eosinophil levels and even increased it [33]. Similarly, in a retrospective analysis of 751 patients from the ISOLDE (Inhaled Steroids in Obstructive Lung Disease in Europe) study, inhaled steroid treatment did not change blood eosinophil levels [34]. In our study, while the blood eosinophil count and percentage decreased after inhaled steroid treatment compared to the baseline, there was a minimal increase at the 45th-day control compared to the 14th-day value. However, whether steroid treatment provides clinical benefits by reducing blood and sputum eosinophil counts remains unclear.
In the study of COPD exacerbations, systemic inflammation markers such as C-reactive protein (CRP), neutrophils, and neutrophil-to-lymphocyte ratio (NLR) are crucial for understanding the underlying inflammatory processes. Elevated CRP levels have been associated with a significantly higher mortality risk in patients with COPD, underscoring its potential role in patient management and risk assessment [35]. Neutrophils, essential for bacterial clearance, are known to be dysfunctionally activated in COPD, contributing to tissue damage and exacerbation severity [36]. Similarly, an increased NLR has been correlated with adverse outcomes, suggesting its utility as a prognostic indicator [37].
Beyond these markers, the role of other mediators such as interleukins (IL-6, IL-8), tumour necrosis factor-alpha (TNF-α), and arginase activity also merit attention. IL-6 and IL-8 are potent mediators of inflammation, often elevated during COPD exacerbations and linked with disease progression and exacerbation severity [36]. TNF-α is another cytokine involved in systemic inflammation and has been associated with more severe health outcomes in patients with COPD [35]. Moreover, arginase activity, which modulates nitric oxide metabolism and airway remodelling, is elevated in exacerbated phases of COPD, contributing further to the inflammatory milieu [38].
Considering these multifaceted aspects, future research should incorporate these diverse inflammatory markers to provide a more comprehensive understanding of the inflammatory pathways in COPD exacerbations. Such studies could potentially lead to more targeted therapeutic strategies, improving management and outcomes for patients with COPD.
The limitations of this study include the small sample size, lack of examination of inflammatory parameters other than eosinophils, and absence of pulmonary function tests. Re-exacerbation and mortality rates could have been evaluated within a 6-month or 1-year follow-up, but time constraints prevented this. However, as a continuation of the study, long-term follow-up is planned by contacting patients or their relatives via telephone.
The absence of pulmonary function tests in this study represents a significant gap in the assessment of COPD exacerbation severity and its correlation with eosinophil levels. Pulmonary function tests, such as spirometry, provide essential information about lung capacity and airflow limitation, which are crucial for accurately diagnosing the severity of COPD exacerbations. The inclusion of these tests in future studies could enhance the clinical relevance of inflammatory markers by allowing researchers to directly correlate changes in eosinophil levels with functional respiratory outcomes.
In conclusion, we assessed the effects of intravenous and inhaled steroids on sputum and blood eosinophil counts in patients hospitalised for severe COPD exacerbations. Our findings indicate that systemic steroid treatment significantly reduces sputum eosinophil counts, suggesting a potential therapeutic benefit in the management of severe COPD exacerbations by targeting eosinophilic inflammation. However, it is critical to acknowledge the limitations of our study, such as its confined hospital setting and the potential for variations in patient response to steroids, which could influence the generalisability of the results. Additionally, the short-term nature of the study restricts our ability to predict long-term outcomes. For clinical practice, we recommend measuring eosinophil levels in patients experiencing severe COPD exacerbations as a routine component of the diagnostic process. This approach can help determine the suitability of systemic steroid therapy, especially in patients with marked eosinophilia. Regular monitoring of eosinophil levels could provide insights into the efficacy of treatment and help in adjusting therapeutic strategies accordingly. Prospective longitudinal studies are necessary to further evaluate the role of eosinophil counts as a biomarker for systemic steroid efficacy in COPD management. Such research would provide deeper insights into the long-term benefits and optimise treatment protocols, enhancing overall patient care in severe COPD exacerbations. By integrating these recommendations, clinicians can make more informed decisions, potentially improving treatment outcomes for patients with severe COPD exacerbations.