The Potential of Fractional Exhaled Nitric Oxide as a Biomarker in Predicting and Optimizing Use of Treatment in Asthma

Asthma affects the respiratory system and causes airway inflammation. The indication of asthma includes a triad of airway inflammation, hyperresponsiveness, and obstruction. Nitric Oxide (NO) is a gas that is exhaled and is a sign of airway inflammation. NO levels in the exhaled breath of patients with type 2 asthma are elevated, and fractional exhaled nitric oxide (FeNO) is an objective biomarker of airway inflammation. Measurements of FeNO are noninvasive, require minimal patient effort, and are easy to collect in clinical settings. The current review is a systematic review performed using PubMed, Science Direct, and Google Scholar according to The Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocol (PRISMA-P) guidelines. This review discusses the entanglement of understanding FeNO measurement and supplementing existing diagnostic and assessment tools for inflammatory lung diseases. Monitoring FeNO can also help identify different asthma phenotypes within the asthma syndrome and suggest the optimal administration of inhaled corticosteroids (ICS) as elevated FeNO levels indicate ICS response. Non-adherence to ICS is a significant contributor to the failure of asthma treatment. A FeNO suppression test can be done to determine non-adherence. FeNO levels should be used with a careful history, conventional spirometric testing with bronchodilator reversibility, measures of bronchial hyperreactivity using methacholine, and other measures of eosinophilic inflammation, such as a peripheral blood eosinophil cell count. FeNO is more sensitive and specific when paired with other lung function tests.