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. Elevated levels of exhaled nitric oxide indicate airway 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. In comparison, FeNO looks at what amount of nitric oxide you are exhaling and can indicate levels of airway inflammation.

Both are useful tools in diagnosing asthma and determining asthma control.

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. 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. Age, gender, weight, and height may impact FeNO results.

One thing to consider is that diet and smoking are factors that can impact results. You should avoid smoking, vaping, alcohol, caffeine, carbonated drinks and highly processed foods at least an hour prior to your test. If you know you will be undergoing a FeNO test, check with your doctor’s office ahead of time to get specific instructions.

Are there other diseases that cause elevated FeNO levels?

FeNO tests are still 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 and guidelines are frequently updated. FeNO should be used in children over the age of 4 and adults. The latest guidelines indicate that FeNO testing should be used in people with asthma who may need asthma treatment. This is in addition to the usual tests performed prior to treatment. FeNO testing should not replace those tests.

It is important to remember that FeNO testing is just one tool in diagnosing and assessing asthma management. No single tool confirms a diagnosis or measures the effectiveness of your asthma management plan.

Work closely with your healthcare provider and follow up regularly to assess how well your treatment is improving your asthma symptoms.