A fractional exhaled nitric oxide test (often called a FeNO test) measures the amount of nitric oxide in your breath. It can detect inflammation in your airways.
Nitric oxide is a gas in the atmosphere, but the body also produces it when there’s inflammation in the airways.
A higher amount of nitric oxide indicates inflammation or swelling in the airways and can help diagnose conditions that result from sensitivity to allergens.
Here’s a look at how nitric oxide tests work and what you can expect.
A nitric oxide test is safe, simple, and typically takes less than 5 minutes to complete.
The test is similar to other pulmonary function tests and involves blowing into a handheld device. You’ll complete testing in your doctor’s office, and you’ll likely receive your results on the same visit.
To get started, a healthcare professional places a clip over your nose, and you place your mouth over a mouthpiece. Next, you’ll inhale deeply and then exhale into the device until you hear a beep. You’ll repeat this process a few times.
Throughout the test, the technician monitors your breathing from a computer.
If you already have a diagnosis and treatment plan for an allergic condition, a doctor may recommend this test to find out how well your treatment is working.
A nitric oxide test doesn’t require much preparation. However, a doctor may recommend avoiding things that may affect the test. This can include:
- caffeine
- alcohol
- smoking
- nitrate-rich foods, including beets and green leafy vegetables
Certain viruses can also increase your nitric oxide levels.
Exhaled nitric oxide is measured in parts per billion. A higher-than-normal level in people not using inhaled corticosteroids is more than 40 or 50 parts per billion for adults and more than 35 parts per billion for children and adolescents.
The results of your test can determine whether there’s swelling or inflammation in your airways. Higher than normal results indicate inflammation.
You may need additional testing to determine the cause of the inflammation, but it may be due to:
Your doctor might use other tools to diagnose you in addition to a fractional exhaled nitric oxide test. They may also listen to your breathing with a stethoscope and listen for wheezing when you exhale.
They might ask about other symptoms, too. Symptoms that can commonly happen along with high nitric oxide levels include:
- coughing
- chest tightness
- difficulty breathing
A doctor might also order the following pulmonary function tests:
Spirometry
A spirometry test measures the amount of air you breathe in and out of your lungs. This helps gauge how well your lungs work.
Similarly to a nitric oxide test, you’ll inhale and exhale into a mouthpiece connected to a machine.
Challenge test
If certain activities or substances trigger symptoms, the doctor might suggest a challenge test.
You’re first exposed to a possible trigger, such as physical activity or an allergen, and then you’ll take a spirometry test.
Bronchodilators
It can be difficult to complete lung function tests on children. So, if a young child has signs of asthma, doctors might first prescribe a bronchodilator. These medications open the airways and make it easier to breathe.
If the medication improves their symptoms, asthma is a likely diagnosis.
Pulse oximetry tests
A pulse oximetry test involves wearing a pulse oximeter on your finger to measure the oxygen in your red blood cells.
Normal oxygen levels indicate healthy lung function, but low levels can indicate a respiratory issue.
Imaging tests
Keep in mind that symptoms of allergic conditions can mimic other conditions like:
A nitric oxide test is considered safe, and there’s a low risk of side effects. But repeatedly breathing in and out might cause lightheadedness in some people.
Coverage for a nitric oxide test depends on whether your insurance provider considers the test “medically necessary” for a diagnosis. You can contact your insurance provider to confirm coverage.
If your policy covers testing, your out-of-pocket responsibility may include copays to your provider and medical deductibles. The deductible is what you pay out-of-pocket before your insurance provider covers diagnostic testing.
The average cost of testing without insurance may be $1,333.
If a nitric oxide test helps confirm a diagnosis, a doctor will next determine the best course of treatment depending on the severity and underlying cause.
Treatment might include:
- an inhaled corticosteroid to reduce airway inflammation
- quick-relief bronchodilators to open the airways
- allergy medication or allergy shots, if allergies trigger your symptoms
If you’ve been diagnosed with an allergic condition, the doctor can also adjust your medication to better manage symptoms. This can include adding an inhaler with a corticosteroid or recommending biologic therapy if you have severe symptoms.
Some allergic and respiratory conditions can make it difficult to breathe and do some types of physical activity. A nitric oxide test is often the first step to diagnosing one of these conditions. Doctors may also use this test to determine how well treatment is working.
This noninvasive test is relatively quick, and in most cases, you can get your results before leaving your doctor’s office.