FeNO Test: What Exhaled Nitric Oxide Can Show in Asthma
FeNO is a breath measurement that can provide information about one type of airway inflammation. It can support, but cannot replace, a full clinical assessment for asthma.
Service update: FeNO testing is not currently available at Australian Polyclinic. Patients with asthma symptoms can still seek a respiratory assessment; spirometry and other pulmonary function tests are available when clinically indicated.
What does a FeNO test measure?
FeNO stands for fractional exhaled nitric oxide. A dedicated analyser measures nitric oxide in a controlled breath out and reports the result in parts per billion (ppb). In some people, higher levels can be associated with type 2, often eosinophilic, airway inflammation. FeNO is one piece of evidence; it does not diagnose asthma by itself.
Inflammatory signal
FeNO offers information about a particular pattern of airway inflammation when interpreted in context.
Not an airflow test
It does not measure how quickly air leaves the lungs, total lung capacity or gas transfer.
Part of an assessment
Symptoms, medical history, medicine use and other tests help explain what a result means.
How is the test performed?
At a centre that offers FeNO, a patient breathes into a dedicated analyser through a mouthpiece, then exhales slowly and steadily at a controlled flow. The test is non-invasive, generally quick and different from the forceful exhalation used for spirometry. The testing centre should explain any preparation instructions.
When might FeNO help?
A clinician may use FeNO as additional information when asthma is suspected, when symptoms continue despite treatment, or when considering a response to inhaled corticosteroids. It may also help frame a discussion about inhaler use and other reasons for poor symptom control. The test is most useful when it answers a specific clinical question.
A FeNO result does not replace spirometry. Spirometry checks airflow; FeNO offers information about an inflammatory signal. A person can have a high FeNO with normal spirometry, or an abnormal spirometry result with low FeNO.
How are FeNO results interpreted?
The American Thoracic Society describes the following general bands. They help a clinician judge the likelihood of eosinophilic inflammation and corticosteroid responsiveness; they are not diagnostic cutoffs for asthma.
| Band | Adults | Children | Clinical meaning |
|---|---|---|---|
| Lower | Below 25 ppb | Below 20 ppb | Eosinophilic inflammation and corticosteroid responsiveness are less likely; asthma is still possible. |
| Intermediate | 25–50 ppb | 20–35 ppb | Interpret cautiously with symptoms, treatment, allergy status and other findings. |
| Higher | Above 50 ppb | Above 35 ppb | Eosinophilic inflammation and corticosteroid responsiveness are more likely in the right context. |
Does a high value prove asthma?
No. A higher value can support type 2 airway inflammation, but allergic rhinitis, allergen exposure and other factors can also influence it. Diagnosis depends on the wider clinical picture, including evidence of variable airflow limitation where appropriate.
Does a low value rule asthma out?
No. Some people with asthma do not have raised FeNO. Inhaled corticosteroids may lower FeNO, and results can vary over time. Do not use a single reading to stop or change treatment.
What can affect a result?
- Inhaled corticosteroid use and adherence
- Atopy, allergic rhinitis and recent allergen exposure
- Smoking and recent respiratory illness
- Age, food, recent exercise and the timing of the measurement
- Testing technique and the device used
Tell the testing clinician about medicines, symptoms and exposures so they can interpret the measurement appropriately.
Which tests answer different questions?
Spirometry measures forced exhaled volume and airflow and may be repeated after a bronchodilator. For an overview of how tests are combined, see our complete pulmonary function testing guide.
What is available at Australian Polyclinic?
FeNO testing is not currently available at Australian Polyclinic. Depending on the clinical question, a respiratory consultation may lead to spirometry, bronchodilator testing, lung volumes, DLCO or another appropriate assessment. See the Australian Pulmonary Function Laboratory, our asthma service, or the Allergy Centre. Testing is chosen for the individual; every patient does not need every test.
Frequently asked questions
What does FeNO stand for?
Fractional exhaled nitric oxide. The test measures nitric oxide in exhaled breath and may provide information about type 2 airway inflammation.
Is the FeNO test painful?
No. It is a non-invasive breath test using a steady, controlled exhalation into a mouthpiece.
Can a FeNO result diagnose or rule out asthma?
No. A high result does not confirm asthma, and a low result does not exclude it. A clinician considers symptoms and other objective tests.
Is FeNO the same as spirometry?
No. FeNO assesses an inflammatory signal; spirometry measures forced airflow and exhaled volume.
Should I stop asthma medicines before testing?
Do not stop prescribed treatment unless your clinician gives you specific instructions. Medicine use can affect interpretation.
Is FeNO testing available at Australian Polyclinic?
No. FeNO testing is not currently available at Australian Polyclinic. Clinical respiratory assessment and other appropriate pulmonary function tests are available.
Concerned about asthma, wheeze or persistent cough?
A respiratory assessment can review your symptoms, triggers, inhaler use and the investigations most likely to help. Learn about care with Dr G Sarwar Chaudhry at Australian Polyclinic.
First Floor, Building 19, CCA, DHA Phase 5, Lahore · Call or WhatsApp 0311 057 3333.