FeNO Testing May Help Diagnose Asthma

Health Professional

One of the many tests used to help physicians diagnose and treat asthma is Fractional Exhaled Nitric Oxide, or FeNO.  It's a simple procedure where the patient exhales into a mouthpiece connected to a computer that measures the amount of Nitric Oxide (NO) present in asthmatic lungs.

It is now common knowledge that all asthmatics have a small amount of chronic (it's always there) inflammation present in their lungs.  When exposed to certain asthma triggers, this inflammation can worsen, resulting in an asthma attack.

According to the American Thoracic Society (ATS), clinical practice guidelines for exhaled nitric oxide levels for clinical application, the following is true of NO:

  • It is produced in the lungs

  • It is present in exhaled breath

  • It plays a key role in virtually all lung biology

  • It has been implicated in the pathophysiology of lung diseases, including asthma

  • It plays a key role as a vasodilator, bronchodilator, neurotransmitter, and inflammatory mediator

FeNO may act as a good diagnostic test for asthma because asthmatic airways have higher levels of airway inflammation compared with non-asthmatic airways, thus resulting in higher FeNO levels.  Because of this, a high FeNO reading may be indicative of asthma.

To control this underlying airway inflammation, physicians will prescribe asthma controller medicines such as inhaled steroids like Flovent, or inhaled steroids in combination with long acting beta adrenergics like Advair and Symbicort, or various other combinations of medications.

Subsequent measurements of FeNO will help a physician determine if the current medicine regime is working, or whether a step up, or step down, in treatment is required.  In other words, the test monitors how well current treatment is working.

RTmagazine.com notes: "FeNO testing is a two-minute point-of-care breath test that can be used to identify patients with allergic airway inflammation. Airway inflammation is widely recognized as the underlying cause of asthma. Using routine FeNO testing to guide therapy, particularly inhaled corticosteroid therapy, for asthma patients has been shown to reduce asthma exacerbations up to 50 percent, according to Aerocrine."

The ATS guidelines note that the test was first introduced in the early 1990s and has advanced markedly since then. However, studies are still ongoing to determine how reliable the test is, and where it might be useful in the clinical setting.

While the test is not yet standard practice in diagnosing and treating asthma, "it adds a new dimension to the traditional clinical tools," said the authors of the guidelines.

They also note that reference values for the various age groups "have been derived from large population studies, but in practice they have limited application."  The main reason here may be because each asthmatic is unique.

So, similar to the recommended usage of peak flow monitoring, the authors recommend that "when monitoring individual patients with asthma and assessing their treatment, achieving 'personal best' rather than 'normal' values is more helpful."

Perhaps there will come a day where every hospital, and every doctor's office, will have the ability to monitor FeNO, which will be used on a more routine basis to diagnose asthma and monitor the effectiveness of the treatment used to control it.

RTmagazine.com reports that one insurance company, Health Care Service Corporation, has decided that it will pay for FeNO testing for asthmatics.  If more insurance companies follow suit, such testing may be commonplace sooner rather than later.


  1. Dweik, Raed A., et al, "An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FeNO) for Clinical Application," American Thoracic Society Documents, 2011, http://www.thoracic.org/statements/resources/allergy-asthma/feno-document.pdf, accessed 3/24/14

  2. "Major U.S. Insurance Provider to cover FeNO test for asthma," rtmagazine.com, http://www.rtmagazine.com/2014/03/us-insurance-provider-feno-test-asthma/, accessed on 4/24/14