Application of FeNO in the diagnostic and therapeutic algorithm of pediatric asthma: From chronic cough and wheeze to personalized management.

Bronchial asthma is the most common chronic respiratory disease in children. Treatment approaches should aim to achieve disease control, reduce limiting symptoms, and improve quality of life. The routine management of patients with asthma relies on the assessment of symptoms (including persistent cough and wheezing) and spirometry results However, these strategies do not consider the level of airway inflammation, which is a fundamental pathognomonic feature of the disease. The use of biomarkers is increasing in an effort to better understand individual asthma pathways (endotyping), offering the potential for personalized treatment with innovative biologics. Elevated levels of fractional exhaled nitric oxide (FeNO) are an indirect marker of T2 airway inflammation. FeNO is one of the few biomarkers that has been implemented in routine clinical practice because of its undeniable advantages, such as accessibility, noninvasiveness, simple implementation, and cost-effectiveness. However, the current scientific evidence in children is insufficient to recommend its universal use in the diagnosis and treatment of all patients. Considering its known limitations, FeNO can enhance therapeutic processes, particularly in children with severe asthma. High FeNO levels predict a good therapeutic response to corticosteroids and selected biologics (e.g., omalizumab and dupilumab) and indicate an increased risk of exacerbation. Similarly, measuring FeNO levels in children with recurrent wheezing can help determine the risk of future asthma development. Various factors contributing to FeNO value variability must be considered when interpreting the results. The lack of robust clinical studies is reflected in inconsistent guidelines from professional societies regarding the use of FeNO in managing childhood asthma. This review aims to evaluate the advantages, disadvantages, and potential applications of FeNO measurements in light of new findings in the field.