Unlocking Asthma Remission: The Role of FeNO in Small Airways

The clinical importance of small airways in asthma management is becoming ever clear, as reflected in contemporary guideline summaries, with new insights revealing their role in achieving remission-like control in selected patients. Innovative biomarkers such as Fractional Exhaled Nitric Oxide (FeNO) are now being harnessed to provide a clearer picture of airway inflammation. This ongoing exploration presents a potent avenue for improving patient outcomes.

The clinical challenge of managing severe asthma, especially when standard therapies fall short in addressing small airways, is well documented. FeNO primarily reflects type 2 airway inflammation and may help identify patients more likely to achieve remission-like control under type 2–targeted therapy. By focusing measurements at a 350 mL/s flow rate (an extended-flow, investigational approach compared with the guideline-standard 50 mL/s), FeNO can probe small airway contributions to disease complexity. Nevertheless, readings can be influenced by factors such as atopy, smoking, and inhaled corticosteroid use, so interpretation should be integrated with symptoms, exacerbation history, and pulmonary function.

The same nitric oxide measurement that signals inflammation can correlate with treatment-responsive type 2 inflammation, a prerequisite for remission-like control in selected patients, bridging diagnostics with therapeutic outcomes. For patients struggling with traditional treatments, FeNO offers a new perspective driven by measurable benefits in small airways. Disruption of small airway inflammation impacts not only symptoms but also patient quality of life, influencing overall asthma control.

Recent studies highlight how FeNO informs practical decisions in asthma care, particularly when small airway involvement is suspected, consistent with guideline interpretations that support FeNO for assessing type 2 inflammation and helping tailor therapy. These insights encourage clinicians to integrate biomarker data with symptoms and lung function when considering step-up therapy or biologic eligibility, rather than relying on a single test. Despite advances, personalized asthma care still falls short for many, underscoring the need to combine FeNO with structured adherence checks and objective measures.

FeNO helps identify T2-high phenotypes, supports adherence checks for inhaled corticosteroids when values remain elevated, and can inform thresholds considered when escalating to biologic therapy. These actions encourage clinicians to integrate biomarker data with symptom scores and spirometry when adjusting treatment. Even with these tools, many patients need individualized plans that combine objective measures with shared decision-making.

FeNO's utility in non-invasively measuring type 2 inflammation is crucial for personalizing treatments and predicting responses to biologics. In adults, values above commonly cited thresholds can suggest T2-high disease). In routine practice, FeNO is measured at a guideline-standard flow of 50 mL/s to assess T2 inflammation, whereas extended or high-flow measurements are primarily used in research to explore small airway contributions. If small airway inflammation is overlooked, even the most robust therapies might misfire, underscoring FeNO's role when interpreted in context. Yet not all traditional markers offer the needed specificity in isolation, so FeNO complements other markers such as blood eosinophils and IgE in personalized therapy.

Key Takeaways:

• Use FeNO alongside symptoms, spirometry, exacerbation history, and blood eosinophils to phenotype T2 inflammation and guide care.
• Remember that 50 mL/s is the guideline-standard FeNO measurement; extended/high-flow measures to probe small airways remain primarily investigational.
• Biomarker-informed care may help some patients reach remission-like control under appropriate therapy, but FeNO alone does not determine remission.
• Interpret FeNO in clinical context, accounting for factors like atopy, smoking, and inhaled corticosteroid use that can influence readings.