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:

1. 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).
2. No likely alternative cause for the respiratory symptoms
3. 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