Fractional Exhaled Nitric Oxide (FeNO) measurement

Fractional exhaled nitric oxide (FeNO) measurement is a non-invasive, rapid, and standardized test used to assess airway inflammation, particularly eosinophilic inflammation. The method is recommended by European professional societies (ERS — European Respiratory Society, EAACI — European Academy of Allergy and Clinical Immunology) and is widely used for the diagnosis and monitoring of bronchial asthma.

Nitric oxide is produced by the respiratory epithelium (bronchi and bronchioles) in response to inflammation. In the presence of inflammatory cells, especially eosinophils, its level increases, making it a useful marker of airway inflammation.

This test complements standard pulmonary function tests (such as spirometry) by providing additional information about the inflammatory status of the airways and helping clinicians better assess the disease.

Indications

• Suspected bronchial asthma
• Bronchial asthma (allergic and non-allergic forms)
• Bronchial hyperresponsiveness
• Overlap syndrome (asthma + COPD)
• Monitoring anti-inflammatory therapy
• Monitoring response to inhaled corticosteroid therapy
• Assessment of treatment adherence
• Evaluation after allergen exposure

Procedure

• The patient takes a deep breath and then exhales slowly and steadily into a специаль device (FeNO analyzer).
• The procedure takes approximately 3–5 minutes, is painless, and non-invasive.
• Results are available immediately.

Contraindications

The test is safe and has no absolute contraindications.
In some cases, it may be difficult to perform if the patient cannot properly execute the exhalation maneuver (e.g., young children or severely ill patients).

Recovery

No recovery is required.
The patient can immediately resume normal activities.

Advantages

• Non-invasive and painless
• Quick to perform
• Immediate results
• Accurate assessment of airway inflammation
• Supports personalized treatment decisions
• Helps monitor therapy effectiveness and adherence

Sources 

https://publications.ersnet.org/content/erj/60/3/2101585
https://publications.ersnet.org/content/erj/66/suppl69/oa1264
https://www.news-medical.net/whitepaper/20250728/An-overview-of-FeNO-guidelines-in-clinical-practice.aspx
https://pmc.ncbi.nlm.nih.gov/articles/PMC4408724/
https://www.thoracic.org/statements/resources/allergy-asthma/feno-document.pdf
https://pubmed.ncbi.nlm.nih.gov/21885636/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4275462/
https://www.niox.com/en/digital-platform/2025-gina-guidelines-updates-on-feno-testing
https://pubmed.ncbi.nlm.nih.gov/32276003/