Fractional exhaled Nitric Oxide levels: an objective indicator for asthma severity

Background: FeNO (Fractional Exhaled Nitric Oxide) is a biomarker for eosinophilic inflammation and is used for diagnosis and monitoring of asthma. Abnormal FeNO [levels above 35 parts per billions (ppb)] indicates significant airway eosinophilia and steroid-responsive airway inflammation. Some children with asthma have extremely high FeNO, yet it is unknown if these levels represent a different asthma phenotype compared to those with mildly elevated FeNO. Aims: To investigate if FeNO levels correlate with clinical phenotype, comorbidity and Pulmonary Function Tests (PFT) in children with asthma and abnormal FeNO. Methods: Anthropometric data, day symptoms, night symptoms, controller/reliever treatment, comorbidity and PFT were correlated with FeNO level in asthma patients with abnormal FeNO. Results: 125 children and adolescents ages 4-18 years with abnormal FeNO were included. No correlation was found between FeNO and controller/reliever treatment, comorbidity and PFT. However, FeNO levels positively correlated with severity for both day and night symptoms (r=0.263 P=0.003 and r=0.211 P=0.021; respectively). Moreover, FeNO level of 80 ppb was found to be the best cutoff to differentiate between patients with mild vs severe day and night symptoms (P=0.01 and P=0.02, respectively). Conclusion: In asthma patients with abnormal FeNO, the levels of FeNO correlated with severity of symptoms. FeNO level of 80 ppb or above may serve as an objective indicator for severe asthma. In the era of personalized medicine these findings may aid in the clinical management of asthma patients.