BACKGROUND

Fractional exhaled nitric oxide (FE) serves as a marker of eosinophil-mediated airway inflammation and has been used in asthma diagnosis, phenotyping, and guidance regarding selection and adjustment of asthma therapy. Studies suggested that FE correlated with asthma symptoms, peripheral blood eosinophil level, blood IgE level, and spirometry indicators of airway obstruction. However, the results are inconsistent across studies.

METHODS

A prospective cross-sectional study was conducted in Queen Mary Hospital among adult patients with severe asthma. Patients had spirometry with bronchodilator reversibility and same-day FE. Asthma control test (ACT) score and blood eosinophil and total IgE levels were measured within 4 weeks of FE and spirometry. The primary outcome was the correlation of FE and spirometric values. The secondary outcomes included the correlation of FE with ACT score, blood eosinophil, and total IgE levels.

RESULTS

One hundred thirty-five severe asthma patients with FE performed were included in the study. FE was negatively correlated with pre-bronchodilator FEV (L) (r = -0.188, p = 0.029), pre-bronchodilator FEV (% predicted) (r = -0.169, p = 0.050), pre-bronchodilator FEV1/FVC ratio (r = -0.269, p = 0.002), and post-bronchodilator FEV/FVC (r = -0.215, p = 0.018). FE was positively correlated with bronchodilator reversibility (mL) (r = 0.248, p = 0.006) and bronchodilator reversibility (%) (r = 0.823, p = 0.002), baseline blood eosinophil level by absolute cell count (r = 0.308, p < 0.001) and by percentage (r = 0.361, p < 0.001).

CONCLUSION

In adult patients with severe asthma, FE might have a negative correlation with the FEV, FEV/FVC ratio, and a positive correlation with bronchodilator reversibility, as well as with blood eosinophil levels.