Why FeNO is Transforming Asthma Diagnosis and Management

Asthma remains one of the world's most common chronic respiratory diseases, affecting more than 350 million people globally. Yet despite advances in respiratory medicine, accurately diagnosing asthma and optimising treatment remains challenging because asthma is not a single disease, it consists of multiple phenotypes and inflammatory pathways (Murugesan et al., 2023).

One of the biggest developments in recent years has been the growing use of Fractional Exhaled Nitric Oxide (FeNO) testing, a rapid, non-invasive biomarker that provides valuable insight into Type 2 airway inflammation. Rather than replacing traditional diagnostic tools such as spirometry, FeNO adds another important layer of clinical information that can improve diagnostic confidence and support more personalised asthma management (Murugesan et al., 2023).

Understanding FeNO

Nitric oxide is naturally produced within the respiratory tract. In patients with Type 2 inflammatory asthma, inflammatory cytokines stimulate increased production of nitric oxide by airway epithelial cells. This excess nitric oxide can be measured in exhaled breath as Fractional Exhaled Nitric Oxide (FeNO).

Higher FeNO levels are generally associated with eosinophilic airway inflammation—the inflammatory pathway that typically responds well to inhaled corticosteroid therapy (Murugesan et al., 2023).

Because the test simply requires a patient to breathe steadily into a handheld analyser, results are available within minutes, making FeNO an ideal point-of-care investigation.

Why FeNO Matters in Clinical Practice

1. Supporting Asthma Diagnosis

Diagnosing asthma is often difficult, particularly in patients with mild disease or intermittent symptoms where lung function testing may appear normal. International guidelines increasingly recognise FeNO as a valuable adjunct when the diagnosis remains uncertain. While FeNO should not be used in isolation, elevated values can strengthen the likelihood of eosinophilic asthma when interpreted alongside symptoms, history and spirometry findings (Murugesan et al., 2023). Importantly, research suggests that FeNO has high specificity, meaning elevated results are particularly useful for supporting ("ruling in") asthma rather than excluding it.

2. Identifying Type 2 Airway Inflammation

Not all asthma is driven by the same inflammatory mechanisms. FeNO specifically identifies Type 2 (T2) airway inflammation, allowing clinicians to determine whether inflammation is likely to respond to corticosteroid therapy. This provides a biological understanding of the patient's disease rather than relying solely on symptom reporting.

3. Predicting Response to Inhaled Corticosteroids

One of the most valuable clinical applications of FeNO is predicting whether patients are likely to benefit from inhaled corticosteroids (ICS). Evidence shows that patients with elevated FeNO levels often demonstrate a significantly better response to ICS therapy than those with lower FeNO values (Murugesan et al., 2023). This enables clinicians to make more informed treatment decisions while avoiding unnecessary medication escalation in patients unlikely to benefit.

4. Monitoring Asthma Control

Asthma symptoms alone do not always reflect the level of underlying airway inflammation.

Patients may feel relatively well while persistent inflammation continues, increasing their future risk of exacerbations. Regular FeNO monitoring allows clinicians to detect ongoing inflammation earlier and assess whether current treatment is adequately controlling the disease (Murugesan et al., 2023).

5. Predicting Future Exacerbations

Several studies reviewed by Murugesan and colleagues found that elevated FeNO levels are associated with:

• Increased risk of asthma exacerbations

• Poorer asthma control

• Lower lung function

• Accelerated decline in respiratory function

When combined with other biomarkers such as blood eosinophil counts and spirometry, FeNO provides even stronger predictive value for identifying patients at higher risk (Murugesan et al., 2023).

6. Improving Medication Adherence

One often overlooked challenge in asthma management is treatment adherence.

Patients may report taking their inhalers regularly, yet persistent inflammation may suggest otherwise. Because FeNO levels typically fall following effective corticosteroid treatment, clinicians can use serial FeNO measurements to identify patients who may not be receiving adequate anti-inflammatory therapy or who require additional education regarding inhaler adherence (Murugesan et al., 2023).

7. Guiding Advanced Biologic Therapy

As severe asthma treatment becomes increasingly personalised, FeNO is playing an expanding role in identifying patients who may benefit from biologic therapies. Research indicates that elevated baseline FeNO levels may predict improved response to several biologic agents, particularly therapies targeting the IL-4 and IL-13 inflammatory pathways, supporting more precise treatment selection (Murugesan et al., 2023).

FeNO Should Never Be Interpreted Alone

Although FeNO is an extremely valuable biomarker, clinicians should remember that various factors can influence results. Elevated FeNO may also occur in conditions such as:

• Allergic rhinitis

• Chronic rhinosinusitis

• Nasal polyposis

Additionally, age, smoking status, viral infections and dietary nitrate intake may influence measurements. For this reason, FeNO should always be interpreted alongside the patient's history, symptoms, physical examination and other diagnostic investigations (Murugesan et al., 2023).

The Future of Precision Asthma Care

Healthcare is rapidly moving towards precision medicine, where treatment decisions are based on objective biomarkers rather than symptoms alone. FeNO represents one of the simplest, quickest and most accessible biomarkers currently available for respiratory medicine. It supports earlier diagnosis, enables more targeted treatment decisions, assists with monitoring disease activity and contributes to improved long-term asthma outcomes.

As evidence continues to grow, FeNO is becoming an increasingly important component of modern asthma management across both primary care and specialist respiratory practice (Murugesan et al., 2023).

Bringing FeNO Testing to South African Healthcare

At Diagno, we are committed to supporting healthcare professionals with innovative diagnostic technologies that improve clinical decision-making and patient outcomes. We are proud distributors of the Bedfont NObreath® FeNO analyser, a trusted point-of-care solution that delivers fast, accurate and non-invasive FeNO measurements to assist clinicians in the diagnosis, monitoring and personalised management of asthma. Whether you are looking to introduce FeNO testing into your practice or expand your respiratory diagnostic capabilities, our team is here to help.

Contact Diagno today to learn more about the Bedfont NObreath® FeNO analyser and how FeNO testing can enhance your respiratory care pathway.

References

Murugesan, N., Saxena, D., Dileep, A., Adrish, M., & Hanania, N. A. (2023). Update on the role of FeNO in asthma management. Diagnostics, 13(8), 1428. https://doi.org/10.3390/diagnostics13081428