Correlation of FENO With Spirometric Measurements and Blood Eosinophil Level in Patients With Severe Asthma

Background

Fractional exhaled nitric oxide (FE_NO) 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_NO 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_NO. Asthma control test (ACT) score and blood eosinophil and total IgE levels were measured within 4 weeks of FE_NO and spirometry. The primary outcome was the correlation of FE_NO and spirometric values. The secondary outcomes included the correlation of FE_NO with ACT score, blood eosinophil, and total IgE levels.

Results

One hundred thirty-five severe asthma patients with FE_NO performed were included in the study. FE_NO was negatively correlated with pre-bronchodilator FEV₁ (L) (r = −0.188, p = 0.029), pre-bronchodilator FEV₁ (% predicted) (r = −0.169, p = 0.050), pre-bronchodilator FEV1/FVC ratio (r = −0.269, p = 0.002), and post-bronchodilator FEV₁/FVC (r = −0.215, p = 0.018). FE_NO 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_NO might have a negative correlation with the FEV₁, FEV₁/FVC ratio, and a positive correlation with bronchodilator reversibility, as well as with blood eosinophil levels.