FeNO testing measures the amount of nitric oxide in your exhaled breath to detect airway inflammation. This simple breathing test helps doctors understand what’s happening inside your lungs when you have asthma or other breathing problems.
For adults, FeNO levels below 25 parts per billion are considered normal, while levels above 50 parts per billion indicate high inflammation that needs treatment.
Understanding your FeNO results can help you and your doctor make better decisions about your asthma care. The test takes less than 10 minutes and gives immediate results.
We’ll explain how the test works, what different number ranges mean, and how doctors use these results to create your treatment plan. Many patients get confused about their FeNO numbers and what they mean for their health.
We’ll break down the normal, intermediate, and high ranges for adults. You’ll also learn how doctors interpret these results alongside your symptoms and other tests to diagnose asthma and monitor your treatment progress.
FeNO testing measures nitric oxide levels in exhaled breath to detect airway inflammation. This simple breathing test helps doctors diagnose asthma and monitor lung health more accurately than traditional methods alone.
What Is FeNO?
FeNO stands for fractional exhaled nitric oxide. This test measures how much nitric oxide we breathe out when we exhale.
The test is simple and quick. We breathe into a special device that measures nitric oxide levels in parts per billion (ppb).
Doctors use FeNO testing for adults and children over five years old. The test works best when other lung tests like spirometry give unclear results.
Key features of FeNO testing:
The device captures our exhaled breath and analyzes it. Higher levels of nitric oxide often mean more inflammation in our airways.
When our airways become inflamed, they produce more nitric oxide. This makes FeNO testing a useful tool for detecting airway inflammation.
High FeNO levels often indicate active inflammation in our lungs. This inflammation commonly happens with asthma and allergic reactions.
Normal vs. elevated FeNO levels:
The test helps doctors see how well anti-inflammatory medications work. Lower FeNO readings after treatment usually mean the inflammation is getting better.
FeNO testing is especially helpful for people with allergic asthma. These patients often show higher nitric oxide levels when their asthma is not well controlled.
Nitric oxide is a gas that our body makes naturally. In healthy lungs, we produce small amounts of this gas.
Our airway cells release more nitric oxide when they detect irritants or allergens. This response is part of our body’s defense system.
The respiratory system uses nitric oxide for several functions:
When inflammation increases, exhaled nitric oxide levels go up too. This makes FeNO testing a reliable way to monitor lung health.
Different factors can affect our nitric oxide levels. Age, height, and gender all play a role in what levels are normal for each person.
The test measures only the nitric oxide that comes from our lower airways. This gives doctors specific information about lung inflammation rather than general body inflammation.
The FeNO test is a simple breathing test that takes just a few minutes to complete. We use specialized devices to measure nitric oxide levels in your exhaled breath, providing immediate results that help us assess airway inflammation.
We make the FeNO testing process comfortable and straightforward for all our patients. The test requires no needles or invasive procedures.
Before your test, we ask you to avoid eating for at least one hour. We also recommend avoiding nitrate-rich foods like leafy greens for three hours before testing.
You should not smoke or use nicotine products for at least one hour before your appointment. We may ask you to temporarily stop certain asthma medications if your doctor determines it’s safe.
During the test, you’ll sit comfortably while our respiratory technician explains each step. We’ll place a nose clip on you to ensure all air flows through your mouth.
You’ll breathe into a mouthpiece connected to our FeNO device. The process is like blowing bubbles in a drink—gentle and steady.
We’ll ask you to:
Most patients complete the test successfully on their first try. We may repeat the test 2-3 times to ensure accurate results.
We use FDA-approved FeNO devices that provide precise measurements of nitric oxide levels. The NIOX VERO is one of the most common devices we use in our practice.
This portable device delivers results within one minute of testing. It measures nitric oxide in parts per billion (ppb) with high accuracy.
The device includes visual and audio cues to help you maintain the correct breathing pattern. A screen shows your progress during the 10-second exhalation.
Key features of our FeNO devices include:
Our devices meet strict clinical standards for accuracy. They undergo regular maintenance and calibration to ensure reliable results.
FeNO testing complements other lung function tests we perform at our practice. Spirometry measures how much air you can breathe in and out, while FeNO testing measures inflammation.
FeNO vs. Spirometry:
We often use both tests together for a complete picture of your lung health. FeNO testing can detect inflammation even when spirometry results appear normal.
Advantages of FeNO testing:
Unlike other tests that require you to blow hard or fast, FeNO testing only requires steady, gentle breathing. This makes it suitable for patients who struggle with more demanding pulmonary function tests.
We measure FeNO levels in parts per billion (ppb) to determine if airway inflammation is present. Adult normal ranges differ from children, with specific cutoff points that help doctors make treatment decisions.
A normal FeNO level in adults is below 25 ppb. This reading shows that airway inflammation is under control.
When we see these low levels, it typically means your asthma management is working well. Your airways are not producing excess nitric oxide.
Normal range characteristics:
Normal levels don’t always rule out asthma completely. Some people with asthma can still have normal FeNO readings.
We consider these baseline measurements important for tracking changes over time. Your doctor will compare future tests to this normal range.
Intermediate FeNO levels fall between 25-50 ppb in adults. These readings require careful interpretation and additional testing.
We call this the “gray zone” because it’s not clearly normal or high. Your doctor needs more information to make treatment decisions.
Intermediate range factors:
Recent allergen exposure can cause temporary increases in this range. Certain medications might also affect these readings.
We often repeat the test or order additional lung function studies. Your symptoms and medical history help us interpret these borderline values.
High FeNO levels are above 50 ppb in adults. These readings strongly suggest significant airway inflammation is present.
We see these elevated levels most often in people with active asthma. The higher the number, the more inflammation we expect to find.
High FeNO implications:
People with eosinophilic asthma often have particularly high readings. We use these results to guide treatment with inhaled corticosteroids.
High levels help us identify patients who will respond well to specific asthma medications. We monitor these numbers to track treatment effectiveness over time.
FeNO test results help doctors determine if your airways are inflamed and guide asthma diagnosis and treatment decisions. Understanding the specific cut-off points and factors that can affect your measurements is essential for proper clinical interpretation.
FeNO results are measured in parts per billion (ppb) and fall into three main categories. Low levels are below 25 ppb for adults and below 20 ppb for children.
These values suggest minimal airway inflammation. Intermediate levels range from 25-50 ppb in adults and 20-35 ppb in children.
These results require careful evaluation alongside other clinical symptoms and tests. High levels are above 50 ppb for adults and above 35 ppb for children.
These values indicate active airway inflammation that typically responds well to inhaled corticosteroids (ICS). We use these measurements to help with asthma diagnosis and determine the likelihood of allergic asthma.
Higher FeNO levels often point to eosinophilic inflammation, which responds better to anti-inflammatory treatments.
The American Thoracic Society established the current cut-off points in 2011. These guidelines remain the standard for clinical practice today.
For asthma diagnosis, we consider:
We also use FeNO for diagnosis and management decisions. Rising levels may indicate poor asthma control or medication non-compliance.
Falling levels often show good response to ICS treatment. These cut-off points help us make more accurate diagnoses when combined with spirometry and clinical symptoms.
Several factors can influence your FeNO results. Smoking significantly lowers FeNO levels, which can mask airway inflammation in people with asthma.
Caffeine and alcohol consumption before testing may affect results. We recommend avoiding these substances for several hours before your test.
Age and gender also play roles. Women typically have lower FeNO values than men.
Children generally show lower baseline levels than adults. Recent respiratory infections, certain medications, and eating nitrate-rich foods can temporarily change your results.
We consider these factors when interpreting your measurements alongside your medical history.
FeNO testing serves as a valuable tool that helps doctors diagnose asthma and monitor how well treatments are working. The test measures airway inflammation levels, which can predict treatment responses and identify different types of asthma.
We use FeNO testing as a supportive tool when diagnosing asthma, especially when symptoms are unclear. The test works best for ruling in asthma rather than ruling it out.
Normal diagnostic ranges include:
There is an intermediate range where results need careful interpretation. For adults, levels between 25-50 ppb require clinical judgment.
For children, levels between 20-35 ppb fall into this gray area. We often track FeNO levels over time rather than relying on one test.
This approach helps us catch asthma cases that might be missed with a single measurement. The test combines well with other diagnostic tools.
When we use FeNO alongside spirometry and symptom assessments, diagnostic accuracy improves significantly.
Role in Asthma Management
We use FeNO testing to guide treatment decisions and monitor how well medications are working. Patients with well-controlled asthma typically show lower FeNO levels over time.
The test helps us determine if current medications need adjustment. Rising FeNO levels may signal the need for increased anti-inflammatory treatment.
Consistently low levels might allow for medication reduction.
FeNO-guided management helps with:
We can identify undertreated inflammation that conventional management might miss. Regular FeNO monitoring allows us to adjust treatments before symptoms worsen.
This proactive approach often prevents asthma attacks and hospital visits.
FeNO levels help us determine what type of asthma a patient has. This information guides our treatment choices and helps predict outcomes.
Allergic asthma typically shows higher FeNO levels. These patients have type 2 inflammation driven by allergens.
They usually respond well to inhaled corticosteroids and allergy treatments. Non-allergic asthma often presents with normal or lower FeNO levels.
These patients may need different treatment approaches. Standard anti-inflammatory medications might be less effective.
We consider FeNO alongside other markers like blood eosinophil counts. When FeNO is above 20 ppb and blood eosinophils exceed 150 cells/μL, type 2 inflammation is likely present.
Understanding asthma type helps us set realistic treatment expectations. It also guides decisions about allergy testing and environmental control measures.
We use FeNO testing to predict and monitor asthma exacerbations. Higher baseline levels are associated with increased risk of future attacks.
Rising FeNO levels often occur before symptoms worsen. This early warning allows us to intensify treatment and prevent full exacerbations.
Key monitoring points:
We track FeNO trends rather than focusing on single values. Patterns over time provide more useful information than isolated measurements.
The predictive value improves when we combine FeNO with traditional asthma assessments.
While we primarily use FeNO testing for asthma diagnosis, several other respiratory conditions can cause elevated nitric oxide levels. COPD patients often show increased FeNO during flare-ups, and allergic rhinitis commonly raises these measurements even without asthma present.
Patients with COPD may have elevated FeNO levels, especially during acute episodes. We see higher readings when airways become inflamed during flare-ups.
Normal COPD FeNO patterns:
The inflammation in COPD differs from asthma inflammation. COPD typically involves neutrophils, while asthma involves eosinophils.
We use FeNO testing to help distinguish between pure COPD and asthma-COPD overlap syndrome. Higher levels suggest an asthma component that may respond better to inhaled steroids.
Allergic rhinitis commonly causes elevated FeNO readings. We often see levels between 25-40 ppb in patients with seasonal or year-round allergies.
The upper and lower airways share similar inflammatory pathways. When your nose reacts to allergens, your lungs often show inflammation too.
Key points about allergic rhinitis and FeNO:
We consider your allergy history when interpreting FeNO results. Elevated levels from allergic rhinitis alone usually stay below 50 ppb.
Several other respiratory diseases can raise FeNO levels above normal ranges. We see elevated readings in lung transplant patients with rejection or infection.
Conditions that may elevate FeNO:
In population studies, less than one-third of people with high FeNO actually had respiratory disease.
Many elevated results come from non-respiratory causes.
FeNO testing is a fast, non-invasive way to understand what’s really happening inside your lungs. Whether you’re newly diagnosed or managing long-term asthma, your FeNO score helps track airway inflammation and guide personalized treatment.
At Gwinnett Pulmonary & Sleep, we use FeNO testing alongside other advanced tools to give you the clearest picture of your respiratory health.
Call 770-995-0630 or book your FeNO test today—and breathe easy knowing you’re in expert hands.
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