Definition and Clinical Features of Asthma

Asthma is a highly heterogeneous disease characterized primarily by chronic airway inflammation. Diagnosis is based on a history of respiratory symptoms, including:

Wheeze
Shortness of breath, chest tightness, and cough.
Variable severity: Airflow obstruction varies based on triggers such as exercise, allergens, weather changes, or viral infections.
Persistent Inflammation: Chronic inflammation can exist even when a patient has been symptom-free for weeks or months, which is why long-term maintenance therapy is crucial.


Diagnostic Workflow for Children Under 5

According to the GINA 2025 (Global Strategy for Asthma Management and Prevention) framework, a definitive diagnosis requires meeting these three criteria:

Recurrent acute wheezing episode(s): Two or more acute wheezing episodes in the past 12 months, or one episode plus asthma-like symptoms between events (e.g., symptoms worse during sleep, or after laughing, crying or activity).
No likely alternative cause for the respiratory symptoms
A timely clinical response to asthma treatment: Significant clinical improvement after using asthma medications, specifically SABA (short-acting beta2 agonists) or a trial of inhaled corticosteroids for 2–3 months.
Note: If these criteria are not met, the condition is classified as "suspected" asthma requiring further observation. Personal history of allergies (e.g., allergic rhinitis) or a family history of asthma are used as supplementary diagnostic factors.



The Role of FeNO (Fractional Exhaled Nitric Oxide)

FeNO is a biomarker used to assess Type 2 airway inflammation.

Diagnostic Support: A FeNO level > 35 ppb in children (or > 50 ppb in adults/adolescents) supports a Type 2 asthma diagnosis when typical symptoms are present.
Limitations: FeNO alone cannot diagnose asthma. It may be elevated in non-asthma conditions like atopic dermatitis or allergic rhinitis, and it may remain normal in specific asthma phenotypes (e.g., obesity-related asthma).
Variables: Levels can be influenced by age, gender, time of day, and smoking status. Testing should be performed when the patient is stable and free from viral infections.


Conclusion

For patients with confirmed or suspected asthma, high FeNO levels can support the decision to start inhaled corticosteroid therapy. Our Pediatric Pulmonary Function Lab offers FeNO testing, which is non-invasive and easy for young children to perform. It serves as a valuable tool for diagnosis, assessing treatment response, and determining prognosis.