Correlation between fractional exhaled nitric oxide and sputum eosinophilia in exacerbations of COPD

Abstract

IntroductionMeasurements of eosinophils in induced sputum and fractional exhaled nitric oxide (FeNO) are noninvasive biomarkers for assessing airway inflammation phenotypes in chronic obstructive pulmonary disease (COPD). Nevertheless, the clinical application of the correlation between FeNO levels and sputum eosinophilia is controversial. The study aimed to investigate the correlation and predictive relationship between FeNO levels and sputum eosinophils in patients with COPD exacerbation. It also examined the relationship between FeNO levels and blood eosinophil percentage.MethodsA total of 163 patients with COPD exacerbation were included in the cross-sectional study. All patients underwent the following on the same day: FeNO test, spirometry, bronchodilator reversibility test, induced sputum, and routine blood test. They were classified as eosinophilic group or noneosinophilic group based on sputum eosinophilic percentage (≥2.5%)/FeNO levels (≥32 parts per billion [ppb]).ResultsFeNO levels and blood eosinophilic percentage were higher in patients with sputum eosinophilia (n=62) compared to those without (31.35 ppb versus 21.43 ppb, P=0.015; 2.71% versus 0.98%, P<0.0001, respectively). Sputum eosinophilic percentage was higher with raised FeNO (n=34) compared to those with FeNO <32 ppb (5.12% versus 3.12%, P=0.007). Eosinophils in induced sputum correlated with both FeNO levels (ρ=0.221, P=0.005) and blood eosinophilic percentage (ρ=0.399, P<0.001). There was no relationship between FeNO and blood eosinophilic percentage. Blood eosinophilic percentage was predictive of sputum eosinophilia (95% confidence interval [CI] =0.65–0.81, P<0.001) at a cutoff point of 0.65% (sensitivity =73%, specificity =61.3%). FeNO levels were predictive of sputum eosinophilia (95% CI =0.53–3,071, P=0.012) at a cutoff point of 17.5 ppb (sensitivity =65.1%, specificity =56.4%).ConclusionThe clinical relevance of this study provides evidence that inflammatory biomarkers, including sputum eosinophilic percentage, FeNO level, and blood eosinophilic percentage, can be used to positively diagnose eosinophilic COPD. The FeNO level and blood eosinophilic counts/percentage, which determine an optimal cutoff for sputum eosinophilia, need more studies.

Blood cell for the differentiation of airway inflammatory phenotypes in COPD exacerbations

“…A cutoff of 2% peripheral blood eosinophils had a sensitivity of 90% and specificity of 60% for identifying a sputum eosinophilia of greater than 3% at exacerbation [19]. Our previous research had revealed that peripheral percentage blood eosinophil (> 0.65%) [11] can be a very good biomarker of sputum eosinophilic airway inflammation in COPD exacerbations (AUC 0.729, sensitivity =74.2%, specificity =61.4%), the optimal cut offs (0.65%) are similar to the result (> 0.55%) in this study. Blood eosinophil ratios, such as ENR, ELR and EMR, also seemingly predicted sputum eosinophilia.…”

“…Peripheral blood cells may be a potential alternative to quantify sputum inflammatory cells to detect airway inflammatory phenotypes. Recent reports have demonstrated the association between sputum and blood eosinophils in COPD [10,11]. And the 2018 Global Initiative for Chronic Obstruction Lung Disease (GOLD) published an evidence-based clinical research guideline that blood eosinophils (> 2%) can predict the risk of exacerbations [1].…”

Relationship between Particulate Matter (PM10) and Airway Inflammation Measured with Exhaled Nitric Oxide Test in Seoul, Korea

“…e FeNO test has been increasingly used because it can easily and noninvasively measure NO. FeNO is also known to be associated with various interleukins, cytokines, and sputum eosinophilia [27,28]. erefore, FeNO is considered a test reflecting airway inflammation and airway hyperresponsiveness [29][30][31].…”

Biomarkers in COPD – Challenging, Real or Illusive

“…Gao levels were predictive of sputum eosinophilia. 58 Validation of assays, however, as well as interpretation of clinical impact require solution before implementation in practice.…”