FeNO Testing: How It Measures Airway Inflammation in Asthma Management
Feb, 4 2026
Did you know that a simple breath test can reveal exactly how inflamed your airways are? For asthma patients, this test-called the FeNO test-can be a game-changer in getting the right treatment. Unlike traditional tests that only measure airflow, FeNO directly shows inflammation levels. This makes it a powerful tool for diagnosis and treatment adjustments.
What is FeNO Testing?
FeNO Testing is a non-invasive diagnostic tool that measures nitric oxide in exhaled breath to assess airway inflammation in asthma. It's based on Nobel Prize-winning research from 1998 that discovered nitric oxide's role in the body. Today, doctors use it to check for eosinophilic inflammation-the type that responds best to steroid treatments.
During the test, you'll take a deep breath in through a filter that removes outside nitric oxide. Then, you'll exhale steadily into a handheld device for about 10 seconds. The device measures the nitric oxide concentration in parts per billion (ppb). The whole process takes less than a minute. No needles, no pain-just a simple breath.
How FeNO Helps in Asthma Management
FeNO testing gives doctors a clear picture of airway inflammation. When your airways are inflamed, they produce more nitric oxide. By measuring this gas in your breath, doctors can see if your asthma is driven by eosinophilic inflammation. This is crucial because treatments like inhaled corticosteroids work best for this type. For example, a patient with frequent attacks might have a FeNO level of 50 ppb. After starting a steroid inhaler, their FeNO drops to 15 ppb-showing the treatment is working. Studies show using FeNO to adjust treatment can reduce asthma exacerbations by up to 50%.
Compared to spirometry, which measures airflow, FeNO targets the inflammation itself. Spirometry might look normal in mild asthma, but FeNO can still show high inflammation. This is why doctors often use both tests together. A 2022 study found combining FeNO with spirometry and symptom checks improves diagnosis accuracy to 76%-much better than any single test alone.
What to Expect During the Test
FeNO testing is quick and painless. Before the test, avoid smoking, eating, drinking (except water), or vigorous exercise for at least one hour. These can affect results. During the test, you'll wear a nose clip to ensure all air goes through the device. You'll take a deep breath in, then exhale steadily into the mouthpiece for about 10 seconds. The device gives real-time feedback, like a visual guide, to help you maintain the right flow. Most people find it easy-87% of patients report it as 'very easy' or 'easy' to perform.
One patient, 'BreathEasy22', shared: 'The FeNO test was surprisingly simple-just blew into a tube like blowing up a balloon slowly. Got results in 30 seconds while my spirometry took 20 minutes with multiple attempts.' This simplicity makes it ideal for children and those with severe airflow issues who struggle with spirometry.
Understanding Your FeNO Results
FeNO results are measured in parts per billion (ppb). For adults, a level below 25 ppb usually means low inflammation. Between 25 and 50 ppb suggests moderate inflammation, and above 50 ppb indicates high inflammation. For children aged 5-12, the cutoffs are slightly lower: below 20 ppb is low, 20-35 ppb moderate, and above 35 ppb high. However, context matters. Smoking can lower FeNO readings by 30-50%, so your doctor will consider your habits and other symptoms.
| Category | Adults (ppb) | Children (5-12 years) |
|---|---|---|
| Low | <25 | <20 |
| Moderate | 25-50 | 20-35 |
| High | >50 | >35 |
Remember, FeNO alone isn't enough for diagnosis. Your doctor will look at your symptoms, medical history, and other tests like spirometry. For instance, a 34-year-old patient was misdiagnosed with chronic bronchitis for seven years. FeNO testing showed 48 ppb, confirming asthma and changing their treatment plan.
Limitations and When to Use Other Tests
FeNO has its limits. It mainly detects type 2 inflammation (eosinophilic), so it won't help for non-eosinophilic asthma. If your asthma is driven by other factors like neutrophils, FeNO might show normal levels even when symptoms are bad. Also, conditions like allergic rhinitis or eosinophilic bronchitis can raise FeNO, leading to false positives.
Dr. Sally Wenzel, Director of the University of Pittsburgh Asthma Institute, cautions: 'FeNO has lower sensitivity, suggesting that it may not be a good biomarker to rule out asthma.' That's why it's never used alone. The National Institute for Health and Care Excellence (NICE) guidelines state FeNO should never be a standalone diagnostic test. Instead, it's part of a bigger picture. For example, a patient with normal FeNO but severe symptoms might need other tests like sputum analysis or blood eosinophil counts.
However, when used correctly, FeNO shines in monitoring treatment. If your FeNO stays high despite medication, your doctor might switch therapies. A 2023 study found patients with high FeNO levels had a 50% lower risk of asthma attacks when treatment was adjusted based on FeNO results.
The Future of FeNO Testing
FeNO testing is evolving fast. In February 2023, the FDA cleared the first smartphone-connected FeNO device, allowing patients to monitor their levels at home. Companies like Circassia (makers of NIOX VERO) and Thermo Fisher (NObreath) are leading this innovation. As biologic treatments for severe asthma become more common, FeNO helps doctors choose the right therapy. For example, high FeNO levels predict better response to drugs like dupilumab.
Market analysts predict the global FeNO testing market will grow to $412.8 million by 2029. Adoption rates vary widely-68% of US pulmonologists use it regularly, compared to 85% in the UK where NICE guidelines mandate availability. Challenges remain, like inconsistent insurance coverage (only 58% of US commercial plans cover it without restrictions) and limited access in rural areas (only 22% of rural US clinics offer FeNO testing).
But experts like Dr. Eugene Bleecker, Director of the University of Arizona Asthma and Airway Disease Research Center, see a bright future: 'As biologic therapies become more targeted and expensive, objective biomarkers like FeNO will become essential for appropriate patient selection and cost-effective care.'
Frequently Asked Questions
Is the FeNO test painful?
No, it's completely non-invasive. You simply breathe into a handheld device. There are no needles or discomfort involved.
How long does the test take?
The actual test takes less than a minute. You'll need to avoid smoking, eating, or exercising for about an hour before the test, but the procedure itself is quick and easy.
Does insurance cover FeNO testing?
Coverage varies. Medicare covers FeNO for asthma management, but private insurers have different policies. Check with your provider to confirm coverage.
Can children take the FeNO test?
Yes, children as young as five can usually perform the test. It's especially helpful for kids who struggle with spirometry because it's simple and non-invasive.
What if my FeNO level is high?
A high FeNO level indicates airway inflammation. Your doctor may adjust your medication, like increasing corticosteroid inhalers. However, they'll also consider other symptoms and tests before making changes.
Andre Shaw
February 4, 2026 AT 16:41FeNO testing is a complete scam. I've had it done multiple times, and the results were useless. Doctors act like it's the holy grail, but in reality, it's just another way to bill you. I remember when I had a reading of 48 ppb, they prescribed steroids, but my symptoms didn't improve. The whole thing is a money grab. They're not even consistent with the numbers-sometimes it's high, sometimes low, but they always have a treatment plan to push. It's all smoke and mirrors. I've read studies that say FeNO has a 30% error rate. Don't trust it. It's a waste of your time and money. I've spoken to other patients who've had similar experiences. The medical industry is in bed with the device manufacturers. They're pushing this test because it's profitable, not because it's accurate. The truth is, there are better ways to assess asthma without relying on this pseudoscience. I've seen people get misdiagnosed because of FeNO results. It's time to wake up and stop falling for this nonsense.