Association between fractional exhaled nitric oxide and peripheral eosinophils in patients with asthma: a retrospective cohort study

BackgroundFractional exhaled nitric oxide (FeNO) and peripheral eosinophils are important biomarkers of Type 2 inflammation in asthma. FeNO reflects airway inflammation, while eosinophil counts indicate systemic eosinophilic activity. Their combined utility in asthma management warrants further investigation. ObjectiveThis study aimed to assess and compare FeNO levels and peripheral eosinophils in asthmatic patients, examining their relationship with disease characteristics and bronchodilator responsiveness (BDR). MethodsA retrospective analysis of 101 adult asthmatic patients at King Abdulaziz University, Jeddah, was conducted. Patient data on FeNO, eosinophil counts, spirometry, and comorbidities were collected and analyzed using correlation and receiver operating characteristic (ROC) curve analysis. ResultsThe mean FeNO level was 68.9{+/-}61.3 ppb, and the mean eosinophil count was 310.5{+/-}344.2 cells/L. FeNO levels were significantly higher in patients with eosinophil counts [≥]300 cells/L (p=0.012) and correlated positively with BDR (r=0.38, p=0.001) but not with eosinophil counts (r=0.16, p=0.11) or asthma control test (ACT) scores. Eosinophil counts were significantly associated with moderate airway obstruction (p=0.041). FeNO showed a borderline ability to differentiate allergic rhinitis (p=0.059) but limited performance in identifying other comorbidities, such as chronic rhinosinusitis (p=0.17), GERD (p=0.87), and eczema/atopic dermatitis (p=0.11 and p=0.24, respectively). ConclusionFeNO and peripheral eosinophil counts are valuable complementary biomarkers for assessing type 2 inflammation in asthma and guiding treatment. However, their variability across clinical contexts underscores the need for integration with other assessments. These findings support a multidimensional approach to asthma management and call for further research to refine their clinical applications.