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Fractional exhaled nitric oxide (FeNO)

Overview

FeNO or fractional exhaled nitric oxide testing has become a valuable tool in the management of asthma, providing clinicians with additional information beyond traditional diagnostic methods.

  • Nitric Oxide (NO) Production: NO is produced by various cells in the respiratory tract, particularly epithelial cells, in response to inflammatory triggers, such as allergens or irritants. Most of the NO present in exhaled air originates from the nasal airways and it can be measured.
  • Airway Inflammation: In conditions like asthma, the levels of NO increase owing to the increased production of an enzyme called inducible nitric oxide synthase (iNOS) in inflamed airway epithelial cells and inflammatory cells (e.g., eosinophils).

The principle behind FeNO testing lies in the relationship between NO production and airway inflammation. Thus, when we breathe out, our breath can show if our airways are inflamed.

In FeNO testing, the amount of NO present in exhaled breath, which correlates with the degree of airway inflammation, is calculated. Elevated FeNO levels suggest ongoing inflammation, whereas lower levels may indicate controlled or less severe inflammation.

Monitoring: FeNO testing serves as a non-invasive method to monitor airway inflammation over time, guiding treatment adjustments and assessing the response to therapy.

Predicting Flare ups: High FeNO levels may indicate an increased risk of asthma flare ups, prompting the initiation of proactive management strategies.

FeNO testing is particularly useful in the following scenarios: 

  • Monitoring Treatment: Assessing the effectiveness of corticosteroid therapy and guiding step-up or step-down in treatment intensity.
  • Identifying Treatment Non-adherence: High FeNO levels despite symptoms can suggest poor adherence to the prescribed corticosteroids.

In asthma management, FeNO testing plays a crucial role in personalising treatment and tailoring medication dosages to the level of airway inflammation indicated by FeNO levels or considering alternative therapies with biologics. FeNO testing enhances the precision of asthma management by providing quantitative data on airway inflammation.

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