FeNO Testing

Fractional Ejection of Nitric Oxide (FeNO) Testing

FeNO testing is a non-invasive test that measures the amount of nitric oxide gas in a person's breath. Nitric oxide is a gas produced by cells in the lining of airways and is an important marker of airway inflammation.

What does a FeNO test diagnose?

This test is useful for diagnosing asthma when spirometry test results are unclear or display a borderline diagnosis. FeNO testing can also detect inflammation in lower airways, including in the bronchioles, and monitor treatment progression. This type of inflammation is caused by higher-than-normal levels of white blood cells (eosinophils) in your lungs. Normally they will be called in to defend against respiratory viruses, but in allergic asthma this response is amplified and uncontrolled leading to chronic inflammation

How is a FeNO test performed?

During this lung assessment, the patient exhales into a device that measures the concentration of nitric oxide in their breath. The test takes only a few minutes to perform and is simple and painless. When the test results are analysed, elevated nitric oxide levels indicate asthma presence. The results may also be used to distinguish between different types of airway inflammation, as elevated FeNO levels are associated with conditions including allergic rhinitis, COPD, and cystic fibrosis. It can indicate the use of a corticosteroid inhaler to dampen inflammation and resolve airway swelling. Normally the particle count should be below 25 parts per billion. 

What Should I Avoid Consuming?

Alongside avoiding all food and drink one hour before your FeNo test, a range of specific items should not be consumed the day of your test as they can skew results. This extensive list includes the following:

How Do I Prepare for a FeNo Test?

For FeNo testing we want to measure a very sensitive particle of gas so we will ask you to be even more careful with what you put into your body before testing. Please do not consume any food or drink for one hour prior to testing. We will also ask you not to consume a specific selection of food and drinks on the day of your test, as they can alter the levels of this gas in your breath. 


  • Spinach
  • Lettuce
  • Beetroot
  • Celery 
  • Chervil
  • Radish
  • Turnips
  • Carrot


  • Citrus fruits
  • Strawberries
  • Currants
  • Raspberries
  • Cherries
  • Gooseberries


  • Ham 
  • Bacon
  • Salami


  • Carbonated drinks
  • Juices
  • Alcohol
  • Caffeine
  • Vitamin C Tablets

Do not engage in exercise or use your corticosteroid inhaler prior to the breathing test. Your corticosteroid inhaler will dampen the inflammation we are trying to measure and may underestimate the severity of your airway inflammation.

If you are unsure on what you should and shouldn't take, please see the table below. 

Preventers (Corticosteroid)

  • Fluticasone (Flovent HFA, Arnuity Ellipta, others)
  • Budesonide (Pulmicort Flexhaler)
  • Mometasone (Asmanex Twisthaler)
  • Beclomethasone (Qvar RediHaler)
  • Ciclesonide (Alvesco) 
  • Fluticasone and salmeterol (Advair Diskus, AirDuo Digihaler, others)
  • Budesonide and formoterol (Symbicort)
  • Mometasone and formoterol (Dulera) 
  • Fluticasone and vilanterol (Breo Elipta)

Do I need a FeNO test?

GPs may refer a patient for FeNO testing if their spirometry results came back unclear, they are experiencing respiratory condition symptoms, or they have recently commenced a new treatment plan.

The FeNO lung function test checks for inflammation of the lung, and how the inhaled steroids are suppressing the inflammation.

For more information about pulmonary function tests, speak to the sleep and thoracic specialists at NBST.

We are happy to assist with the diagnosis and treatment of lung conditions, breathing symptoms, and respiratory conditions.

Our doctors are on hand to assist with respiratory and sleep testing, diagnosis and treatment.

Contact us to book an appointment

Visit us at either our Clayfield or North Lakes location and experience compassionate care in a comfortable environment, tailored to meet your unique needs.