A 28-year-old woman with a 5-year history of asthma presents with recurrent exacerbations despite regular inhaled corticosteroid therapy. She reports symptoms 3–4 times per week and nocturnal awakening twice weekly. Her baseline FEV₁ is 72% predicted. Which investigation is most appropriate to assess asthma control and guide escalation of therapy?

## Investigation of Choice for Asthma Control Assessment **Key Point:** Exhaled nitric oxide (FeNO) is a non-invasive biomarker of eosinophilic airway inflammation and is increasingly used to assess asthma control, predict response to inhaled corticosteroids (ICS), and guide treatment escalation in patients with inadequate control despite therapy. ## Why FeNO is the Best Choice ### Clinical Utility in This Scenario - FeNO >25 ppb indicates active eosinophilic airway inflammation and predicts good ICS responsiveness - Elevated FeNO in a patient on regular ICS suggests either poor adherence or ICS-resistant asthma - Helps differentiate true asthma from other conditions mimicking asthma (e.g., vocal cord dysfunction, GERD-related cough) - Non-invasive, rapid, and reproducible ### Role in Management 1. **Baseline assessment** — establishes inflammatory phenotype 2. **Monitoring** — tracks response to ICS dose escalation 3. **Adherence assessment** — persistently elevated FeNO despite reported compliance suggests non-adherence or steroid resistance 4. **Phenotyping** — identifies eosinophilic asthma (FeNO >25 ppb) vs. non-eosinophilic phenotypes **High-Yield:** FeNO-guided therapy has been shown to reduce exacerbation rates and optimize ICS dosing in patients with inadequate asthma control. It is now recommended by GINA 2023 and NAEPP guidelines as an adjunctive tool for asthma management. **Clinical Pearl:** In this patient with persistent symptoms despite ICS therapy, FeNO measurement would clarify whether: - ICS dose needs escalation (if FeNO elevated) - Adherence is the issue (if FeNO elevated despite reported compliance) - Alternative diagnoses should be considered (if FeNO normal) ## Comparison with Other Investigations | Investigation | Indication | Why Not Here | |---|---|---| | **Spirometry + bronchodilator** | Baseline lung function, reversibility testing | Already done; FEV₁ 72% known. Does not assess current inflammation or guide therapy escalation. | | **Methacholine challenge** | Diagnose asthma in symptomatic patients with normal spirometry | Patient already has confirmed asthma diagnosis; challenge testing not needed for management. | | **HRCT chest** | Rule out alternative diagnoses (bronchiectasis, ILD, emphysema) | No clinical indication in uncomplicated asthma; reserved for atypical presentations. | [cite:GINA 2023 Global Strategy for Asthma Management]