ATS Guideline on Exhaled Nitric Oxide Levels (FENO) Use

Measurement of fractional nitric oxide (NO) concentration in exhaled breath (FENO) is a quantitative and noninvasive method of measuring airway inflammation.

The American Thoracic Society (ATS) aimed to develop evidence-based guidelines for the interpretation of FENO measurements. According to them, in the setting of chronic inflammatory airway disease including asthma, conventional tests such as FEV1 reversibility or provocation tests are only indirectly associated with airway inflammation.

However, a 2012 study in the journal Thorax, showed that tailoring of asthma treatment based on FeNO levels was ineffective in improving outcomes in children and adults.

FENO offers added advantages for patient care including:

- detecting of eosinophilic airway inflammation
- determining the likelihood of corticosteroid responsiveness
- monitoring of airway inflammation to determine the potential need for corticosteroid
- unmasking of otherwise unsuspected nonadherence to corticosteroid therapy

FENO levels above 50 parts per billion (ppb) suggest the presence of eosinophilic airway inflammation and likely responsiveness to inhaled corticosteroids. FENO levels below 25 ppb suggest that eosinophilic airway inflammation is unlikely and that the individual is not likely to respond to treatment with (or increasing the dose of) inhaled corticosteroids depending on the clinical context.

FENO cut-points

The guidelines propose a series of cut-points to help make clinical decisions:

- FENO lower than 25 ppb (lower than 20 ppb in children) indicates that eosinophilic inflammation and responsiveness to inhaled corticosteroids are less likely.

- FENO higher than 50 ppb (higher than35 ppb in children) indicates that eosinophilic inflammation and, in symptomatic patients, responsiveness to inhaled corticosteroids are likely.

- FENO values between 25 ppb and 50 ppb (20-35 ppb in children) should be interpreted cautiously with reference to clinical context.

What is a significant change in FENO?

FENO increases of 20% or more for values over 50 ppb (or 10 ppb more for values less than 50 ppb) are significant, from one visit to the next. Conversely, reductions of 20% or 10 ppb indicate significant response to anti-inflammatory therapy.

Videos by the manufacturer of the FENO measurement device Niox Mino, Aerocrine:


An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications. American Journal of Respiratory and Critical Care Medicine Vol 184. pp. 602-615, (2011). Full text PDF.
ATS Publishes Clinical Practice Guidelines on Interpretation of FENO Levels
Practical points on using NIOX MINO fractional exhaled nitric oxide (FENO) measuring device
Inflammometry: the current state of play in asthma - FeNO and more. Thorax, 2012.
In the UK, FeNO is used in primary practice to guide ICS initiation, dosing and identify poor ICS adherence
Image source: NioxMino.

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