The value of inflammatory biomarkers in differentiating asthma-COPD overlap from COPD

Purpose: To evaluate the accuracy of inflammatory biomarkers in differentiating patients with asthma-COPD overlap (ACO) from those with COPD alone. Methods: Clinical data of 134 patients with COPD and 48 patients with ACO admitted to the First Affiliated Hospital of Xi’an Jiaotong University from January 2016 to June 2019 were retrospectively analyzed. Receiver operating characteristic (ROC) curve analysis was performed to determine the best cut-off values of fractional exhaled nitric oxide (FeNO), blood eosinophil counts (EOS), and neutrophil to lymphocyte ratio (NLR) for differentiating between ACO and COPD alone. Spearman correlation analysis was conducted to evaluate the relationships between these inflammatory biomarkers and the forced expiratory volume in one second/prediction (FEV 1 %pred). Results: FeNO and EOS in the ACO patients were significantly higher than those in the COPD patients (FeNO: median 37.50 vs 24.50 ppb, P < 0.001; EOS: median 0.20 vs 0.10 ×10⁹ /L, P = 0.004). FeNO was positively correlated with FEV ₁ %pred (r = 0.314, P = 0.030), while NLR was negatively correlated with FEV 1 %pred (r = -0.372, P = 0.009) in patients with ACO. In addition, a positive correlation between FeNO and EOS was also found in ACO, especially in patients without history of inhaled corticosteroids (ICS) use (r = 0.682, P < 0.001). The optimal cut-off value of FeNO was 31.5 ppb (AUC = 0.758, 95% CI = 0.631-0.886) in patients with smoking history, with 70.0% sensitivity and 89.9% specificity for differentiating ACO from COPD. In patients without history of ICS use, the best cut-off value of FeNO was 39.5 ppb (AUC = 0.740, 95% CI = 0.610-0.870), with 58.3% sensitivity and 84.9% specificity. Among patients without history of ICS use and smoking, 27.5 ppb was optimal cut-off level for FeNO (AUC = 0.744, 95% CI = 0.579-0.908) to diagnose ACO, with 81.8% sensitivity and 60.7% specificity, and the sensitivity was improved to 91.7% when FeNO was combined with EOS. Conclusion: The inflammatory biomarkers FeNO and EOS can be used as indicators for differentiating between ACO and COPD alone.