Asthma and other breathing problems can be tricky to pin down. Coughing, wheezing, chest tightness, and shortness of breath are common symptoms, but they don’t always mean asthma, and even when asthma is suspected, confirming the diagnosis can take time.
At Kent Family Medical, we use a range of diagnostic tools to give you clear answers and the right treatment plan.
One of these is FeNO testing: a quick, painless test that measures airway inflammation and helps us understand what’s happening inside your lungs.
Here, we’ll explain what FeNO testing is, when it’s recommended, and how it compares with another common lung test, spirometry.
What Is FeNO Testing?
FeNO stands for Fractional exhaled Nitric Oxide. Nitric oxide is a gas that your body naturally produces, and higher levels in the breath can indicate inflammation in the airways, which is often linked to asthma.
During the test:
- You simply breathe into a handheld device through a mouthpiece.
- The machine analyses your breath and gives an instant result.
- It takes just a couple of minutes, is completely painless, and involves no needles or invasive procedures.
If your FeNO level is raised, it suggests that inflammation is present. This information helps our GPs to:
- Support an asthma diagnosis.
- Decide whether inhaled corticosteroids (a common asthma treatment) are likely to help.
- Monitor how well your current treatment is working.
When Is FeNO Testing Recommended?
FeNO testing isn’t needed for everyone with breathing problems, but it can be very useful in certain situations. Our GPs may recommend FeNO if:
- Asthma is suspected but not confirmed – for example, if you have symptoms but require a definitive diagnosis.
- Assessing whether steroid inhalers are required – a raised FeNO level with symptoms of asthma can help to guide treatment decisions.
- Checking asthma control – repeated FeNO tests over time can show whether inflammation is improving, or if your treatment needs adjusting.
- Avoiding unnecessary medication – if your FeNO level is normal and there is a low level of clinical suspicion, this may provide further reassurance that steroid inhalers are unlikely to help and an alternative diagnosis is more likely.
It’s important to know that FeNO is just one part of the picture. At Kent Family Medical, we always combine test results with your history, symptoms, and examination to give a complete and accurate assessment.
What Is the Difference Between Spirometry and FeNO Test?
Both FeNO and spirometry are commonly used in asthma diagnosis and management, but they look at different aspects of lung health and are now recommended at different points in the diagnostic pathway:
| Feature | FeNO Test | Spirometry |
| What it measures | Airway inflammation (nitric oxide levels) | Lung function (airflow and lung capacity) |
| How it works | Breathing steadily into a device | Blowing forcefully into a machine |
| Time taken | Quick (a couple of minutes) | 30-45, requires repeated effort and is performed before and after a blue inhaler |
| Effort required | Minimal – calm, steady breath | More effort – forceful blowing needed |
| Clinical use | Shows if inflammation is present; first-line test for asthma | Detects airflow obstruction; monitors lung capacity; supports diagnosis of asthma, COPD, and restrictive lung disease. |
| Best for | First-line diagnostic test and guiding treatment decisions in asthma | Diagnosing airflow limitation and tracking long-term lung health |
In practice, these two tests complement each other. Spirometry tells us how well your lungs are working, while FeNO shows us what’s happening at an inflammatory level. Together, they provide a fuller picture of your respiratory health.
If there is a strong clinical suspicion of asthma and your FeNO is normal, your clinician may suggest spirometry to see if this more detailed picture suggests asthma.
Practical Considerations: What Patients Can Expect
One of the main advantages of FeNO testing is how simple it is for patients (it can be carried out on patients as young as 5).. Here’s what you can expect at Kent Family Medical:
Before the Test
We ask you to prepare for FeNO testing:
24hrs Prior
- It is recommended to avoid alcohol consumption for 24 hours before the test
12hrs Prior
- It is recommended to avoid smoking for 12 hours before the test*
- It is recommended to avoid eating foods high in nitrates, which include, but are not limited to:
- Arugula, Spinach, Lettuce, Radish, Beetroot, Chinese cabbage, Turnips, Cabbage, Green beans, Leek, Spring onion, Cucumber, Carrot, Potato, Garlic, Sweet pepper, Green pepper
Day of the Test:
- On the day of the test, it is recommended to avoid any of the following 1 hour before the test:
- Eating, Drinking, Smoking, Exercise
During the Test
- You’ll be asked to sit comfortably and breathe steadily into a handheld device.
- Unlike spirometry, you don’t have to blow forcefully – just a calm, steady breath.
- The test itself only takes seconds..
After the Test
- Your results are available straight away, but may require review by our doctor afterwards.
- Our clinician will discuss them with you in the context of your symptoms and overall health.
- There are no side effects, and you can return to your usual activities immediately.
Who Performs the Test?
At Kent Family Medical, FeNO testing is carried out by our experienced Nurse, either as a standalone test or as part of a comprehensive asthma assessment. GP input will usually be required pre- or post-test.
Final Thoughts
FeNO testing is a safe, quick, and non-invasive way of measuring airway inflammation, making it a valuable tool in diagnosing and managing asthma.
It is now the first-line diagnostic test in patients with suspected asthma, before spirometry, and helps our doctors personalise your care and ensure you get the right treatment.
If you or your child is experiencing breathing difficulties and asthma is suspected, our GPs at Kent Family Medical may recommend a FeNO test as part of your assessment.
To arrange an appointment or to learn more about FeNO testing at Kent Family Medical, please get in touch with our team today.