The correlation of Fractional Exhaled Nitric Oxide (FeNO) level with the absolute Eosinophil count and level of Bronchial Asthma control: A prospective cross sectional study

Abstract

Patients with asthma have high levels of Nitric Oxide (NO) in their exhaled breath and elevated blood eosinophil counts. No study identifying the correlation of FeNO and absolute eosinophil count with the level of bronchial asthma control has been done among Filipinos. We determined the correlation between the fractional exhaled Nitric Oxide levels, and absolute blood eosinophil count with levels of asthma control. Spirometry was done for participants who were diagnosed with asthma based on symptoms only. FeNO analysis was performed on the same visit. Eosinophil counts were collected and recorded. Correlation between Asthma severity and FeNO levels was determined and tested using Spearman correlation analysis. The level of significance was set at 0.05. Older age groups (mean age 60) had the tendency to develop uncontrolled asthma, and higher FeNO levels. Higher FeNO levels were strongly correlated with uncontrolled asthma, r=0.78 and was highly sensitive and specific in predicting uncontrolled Bronchial Asthma. On the other hand, the difference in the absolute eosinophil count among the groups was not statistically significant, p=0.90, but still revealed a weak positive correlation, r=0.33. This study was able to ascertain that FeNO levels equal or above 41 ppb is associated with uncontrolled Asthma. Although absolute eosinophil count above or equal to 0.4 ×109/L is sensitive in predicting uncontrolled asthma, this parameter was not specific. Hence, an elevated FeNO measurement is more sensitive in accurately predicting uncontrolled asthma as compared to absolute eosinophil counts.