From the Guidelines
FENO (Fractional Exhaled Nitric Oxide) is a biomarker test that measures the level of nitric oxide in a person's breath, primarily used to assess airway inflammation in asthma patients, as supported by the most recent and highest quality study 1.
What is FENO?
FENO testing involves breathing into a handheld device that analyzes the nitric oxide concentration, with results typically available within minutes.
- Normal FENO values are generally below 25 parts per billion (ppb) for adults and below 20 ppb for children,
- while elevated levels (>50 ppb in adults) suggest active eosinophilic airway inflammation, as indicated by 1.
Clinical Applications of FENO
FENO testing helps clinicians:
- diagnose asthma,
- predict responsiveness to inhaled corticosteroids,
- monitor treatment effectiveness, and
- assess medication adherence, as stated in 1. The test works because inflammatory cells in the airways of asthmatic patients produce nitric oxide, which increases during inflammation and decreases with effective anti-inflammatory treatment.
Importance of FENO in Asthma Management
FENO testing is particularly valuable for distinguishing between different asthma phenotypes and guiding personalized treatment approaches, though results should always be interpreted alongside clinical symptoms and other diagnostic tests, as recommended by 1 and 1.
- The use of FENO can support a diagnosis of asthma,
- determine the likelihood of steroid responsiveness,
- and monitor treatment effectiveness, as supported by 1. In summary, FENO is a useful biomarker for assessing airway inflammation in asthma patients and guiding personalized treatment approaches, as supported by the most recent and highest quality study 1.
From the Research
Definition of Fractional Exhaled Nitric Oxide (FENO)
- Fractional Exhaled Nitric Oxide (FENO) is a marker of airway inflammation 2
- FENO is a non-invasive surrogate biomarker for the assessment of eosinophilic airway inflammation 3
- FENO can be used to identify patients with eosinophilic inflammation who would potentially respond to corticosteroid therapy 4
Clinical Utility of FENO
- FENO can be used in the initial diagnosis of asthma and aid in stratification of which patients would be steroid responsive 4
- FENO can be used to assess disease severity, response to treatment, and compliance 4
- FENO testing is a cost-effective procedure and has been shown to improve patient management when combined with standard assessment methods 5
- FENO may also be useful as a surrogate biomarker for the assessment and management of severe asthma and to predict responsiveness to some biological therapies 5
Relationship between FENO and Asthma Burden
- Higher FENO levels are associated with greater asthma burden, including more short-acting beta-agonist (SABA) dispensings and oral corticosteroid (OCS) use 2
- FENO levels correlate with serum eosinophil counts, asthma control test (ACT) scores, and FEV1 percentage predicted 3
- High FENO levels are associated with an increased risk of having an abnormal FEV1 percentage predicted 3
Guidelines and Recommendations
- The American Thoracic Society (ATS) recommends FENO as part of the initial diagnosis of asthma and for monitoring of airway inflammation 6, 5
- The National Institute for Health and Care Excellence (NICE) guidelines recommend the use of FENO for the initial diagnosis of patients with suspected asthma 5
- A conditional recommendation for FENO-based care has been made, suggesting that FENO is beneficial and should be used in addition to usual care 6