What is FeNO in Asthma?
One of the tests used for people with asthma is a fractional exhaled nitric oxide (FeNO) test. Your body makes nitric oxide (a gas), which gets released when you breathe out or exhale. A FeNO test measures the level of nitric oxide in your breath. High levels of exhaled nitric oxide indicate airway inflammation.
FeNO tests can be used to help diagnose asthma. They can also be used for asthma management. For example, FeNO tests can evaluate how well inhaled corticosteroids are working to calm airway inflammation.
FeNO tests can be used in people with mild asthma or moderate to severe asthma. They can be used in people with allergic asthma and eosinophilic asthma.
Ask your doctor or asthma specialist for a FeNO test at your regular visit, especially if you think there’s underlying inflammation in your airways. Two devices used for FeNO tests are the Vitvatmo pro and the NIOX VERO®.
Why is FeNO elevated in asthma?
Asthma begins with inflammation. The lining of the airways becomes swollen, inflamed and clogged with mucus and fluid.
Asthma inflammation is the quiet part of asthma. When we talk about quiet asthma, that’s when the inflammation and swelling takes place. You can’t feel or see what’s going on. But each time your airways are exposed to your asthma triggers, the inflammation may increase. And your symptoms may get worse.
High FeNO levels indicate your airways are inflamed or irritated. This is why FeNO testing is a valuable tool for asthma management. It can help doctors determine which medication and treatment is best for you and your asthma symptoms. It can also help determine if you are at risk for asthma exacerbations.
FeNO can be used in asthma diagnosis when combined with your medical history, physical exam, and other tests such as spirometry. But an elevated FeNO test alone cannot confirm an asthma diagnosis. Other medical conditions can cause high FeNO levels.
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What FeNO devices are available?
Here are two FeNO medical devices commonly used by healthcare professionals:
Vivatmo pro
Vivatmo pro is a non-invasive device to measure FeNO levels in a patient’s breath. Developed by Bosch Healthcare Solutions, the device is distributed by Methapharm Respiratory in the United States. Designed for patients ages 7 and up, the device includes a portable handle and provides real-time insights into airway inflammation. It filters out particles, bacteria, viruses and moisture to ensure the breath sample is optimal for accurate measurement. Results are displayed on screen within seconds and can be added to digital patient records.
NIOX VERO®
NIOX VERO is a non-invasive FeNO device that assesses airway inflammation at the point-of-care. The device requires patients to inhale – at a steady flow rate – through a breathing handle. The handle helps patients exhale a sample of air not contaminated by viruses and bacteria. It also has tubing to filter out excess humidity from patient breath. The device gives an accurate, real-time measurement of FeNO levels, with results displayed on screen.
What is a normal FeNO level?
In clinical practice, a normal FeNO test is any number less than 25 parts per billion (ppb) in adults. For children, anything less than 20 ppb is considered normal.
What does a high FeNO test mean?
You may be asking, what causes a high FeNO? Just because you have an elevated FeNO does not necessarily mean you have asthma. What it does suggest is that you may be experiencing some level of airway inflammation. And airway inflammation is often an indicator of asthma.
Your healthcare provider will want to look at your symptoms, history, and other tests for asthma to make a diagnosis.
What is FeNO in asthma patients?
A FeNO of 25-50 ppb in adults (20-35 ppb in children) is considered an intermediate range. Numbers in this range should be matched with the medical history and testing. FeNO numbers of over 50 ppb in adults (over 35 ppb in children) are considered high and indicate airway inflammation.
FeNO testing is also a helpful tool in ongoing asthma management and control. Patients with well-controlled asthma typically have lower levels of exhaled nitric oxide. While patients with uncontrolled asthma may have a number of over 30 ppb, FeNO levels may also be elevated during asthma exacerbations.
You and your healthcare provider can use FeNO test results to confirm an asthma diagnosis. The results can also be used to verify how well your daily corticosteroid inhaler is controlling inflammation.
FeNO vs. spirometry
Many patients with asthma are familiar with spirometry testing for asthma. You may be asking, what is the difference between FeNO and spirometry?
Spirometry tests your lung function. It measures your inhalation, exhalation, and how fast and easy you can exhale. Lung function tests are helpful in measuring how well your lungs are functioning.
FeNO looks at the amount of nitric oxide you are exhaling. The test reveals your levels of airway inflammation.
How is a FeNO test done?
FeNO tests are performed at a doctor’s office. The FeNO measurement device consists of a mouthpiece with a tube attached to a measurement device. You breathe through a mouthpiece and exhale slow and steady, for about 10 seconds. The device then measures the amount of FeNO you exhale. You often repeat the test a few times, but it should take less than 5 minutes.
Are there things that can affect FeNO test results?
Like most other tests, results can vary depending on several factors. For example, age, gender, weight, and height may impact FeNO results.
Diet and smoking are also factors that can impact results. You should avoid smoking, vaping, alcohol, caffeine, carbonated drinks and highly processed foods at least one hour prior to your test. If you know you will be undergoing a FeNO test, check with your doctor’s office ahead of time for instructions.
Are there other diseases that cause elevated FeNO levels?
FeNO tests are primarily associated with asthma testing and monitoring. But there are other conditions that may cause elevated levels of exhaled nitric oxide. These include:
- Allergic rhinitis
- Chronic obstructive pulmonary disease (COPD)
- Obstructive sleep apnea
- Interstitial lung diseases (such as pulmonary fibrosis)
Who should undergo FeNO testing?
FeNO testing is used routinely in asthma diagnosis and management. The latest guidelines recommend FeNO testing in addition to the usual asthma treatment and care. FeNO is used in adults and children ages 4 and older.
FeNO testing is just one tool for diagnosing asthma and assessing a management and treatment plan. No single tool confirms a diagnosis or measures the effectiveness of your treatment plan.
Work closely with your healthcare provider to assess your asthma. Follow up regularly to determine how well your treatment is working.
Are there other conditions that may look like asthma or complicate asthma?
There are other types of respiratory conditions that are different than asthma. The symptoms, diagnosis and treatment can vary depending upon the condition. Here are some of them.
Reviewed by:
Bradley Chipps, MD, FACAAI, is a board-certified allergist and pediatric pulmonologist with Capital Allergy and Respiratory Disease Center in Sacramento, California. He earned his medical degree from University of Texas Medical Branch in Galveston in 1972. He is Past President of the American College of Allergy, Asthma and Immunology (ACAAI).
