FeNO in Practice
FeNO testing is now a key part of everyday asthma assessment across UK healthcare. From GP surgeries to specialist respiratory clinics, FeNO offers clinicians a fast, reliable way to measure airway inflammation and make clearer treatment decisions. The following sections explain how FeNO is used in different settings and how it compares with other common diagnostic tools.
FeNO in Primary Care
Primary care is one of the main settings where FeNO testing makes a significant difference. Many patients present with symptoms that overlap with other respiratory conditions, and FeNO provides an objective measure of inflammation that supports more accurate asthma diagnosis.
In GP surgeries and Primary Care Networks, FeNO helps clinicians
• identify eosinophilic airway inflammation
• decide when inhaled corticosteroids are appropriate
• monitor asthma control over time
• reduce unnecessary steroid prescribing
• support NG245 diagnostic requirements
FeNO is quick to perform, easy to interpret and ideal for busy primary care pathways.
FeNO in Secondary Care
In secondary care and specialist respiratory services, FeNO is used to support more complex asthma cases. It helps clinicians understand the type and severity of airway inflammation and guides decisions around advanced treatments.
Secondary care clinicians use FeNO to
• support diagnosis when symptoms are difficult to interpret
• assess steroid responsiveness
• identify patients who may require specialist therapies
• track treatment outcomes during follow up
• support severe asthma pathway assessments
FeNO provides a clear biomarker that complements more detailed investigations carried out in hospital settings.
FeNO vs Spirometry
FeNO and spirometry measure different aspects of airway health and are most effective when used together.
Spirometry assesses airflow obstruction by measuring lung function. It is useful for diagnosing conditions like COPD and for identifying airflow limitation in asthma. However, spirometry cannot detect airway inflammation.
FeNO measures nitric oxide levels, which reflect eosinophilic inflammation linked to asthma. It helps determine whether inflammation is present even when spirometry results appear normal.
In practice
• Spirometry = how well the lungs are working
• FeNO = how inflamed the airways are
Using both tests provides a fuller picture for diagnosis and monitoring.
FeNO vs Eosinophils
Both FeNO testing and eosinophil blood tests can help identify eosinophilic inflammation, but they offer different advantages.
Eosinophil blood tests measure the number of eosinophils in the bloodstream, which can indicate systemic inflammation. However, results can be influenced by infections, allergies or other factors, and results are not specific to the airways.
FeNO directly measures inflammation within the airways themselves. It provides immediate results at the point of care and reflects how likely a patient is to respond to inhaled corticosteroids.
In summary
• Eosinophils = systemic inflammation (blood sample required)
• FeNO = airway inflammation (breath test with instant result)
FeNO is therefore more practical for rapid asthma diagnosis and ongoing management, especially in primary care.