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An introduction to international guidelines for FeNO testing.

In the last few decades, a large number of studies have been carried out to inform how to test and interpret fractional exhaled nitric oxide (FeNO) levels. Based on these results, international authorities such as the American Thoracic Society (ATS), Global Initiative for Asthma (GINA) and the National Heart, Lung and Blood Institute (NHLBI) have compiled guidelines for practitioners to include FeNO in their diagnostic and management processes.1,2,3 In this article we give an overview of the most important aspects of those guidelines.

Many studies have provided evidence that FeNO is a helpful biomarker in diagnosing eosinophilic airway inflammation.4 However, it is important to measure these levels correctly and interpret the results with care. Based on the current insights, international guidelines aim to guide healthcare professionals through this process.

FeNO in the ATS, GINA and NICE guidelines1,2,3

All guidelines recognize the added value of FeNO testing within asthma diagnosis and management.

For asthma diagnoses, the ATS guidelines point out that high FeNO (≥50 ppb for adults, ≥35 ppb for children) indicates eosinophilic airway inflammation, which is often the background pathology of asthma. Therefore, the ATS sees FeNO as supportive for asthma diagnosis.

NIOX Clinical Guidelines for the Interpretation of FeNO..

NIOX Clinical Guidelines for the Interpretation of FeNO.

Both the ATS and GINA guidelines state that FeNO values can help to determine the likelihood of a patient’s corticosteroid responsiveness. Low FeNO values (≤25 ppb for adults, ≤20 ppb for children) indicate that eosinophilic inflammation and responsiveness to corticosteroid treatment is unlikely. High FeNO levels (≥50 ppb for adults, ≥35 ppb for children) point in the opposite direction, suggesting that eosinophilic inflammation and responsiveness to corticosteroids is likely. Intermediate FeNO measurements between 25 and 50 ppb (20 and 35 for children) should be interpreted carefully.

The GINA guidelines state that these measurements mainly apply to ICS responsiveness in the short term. Therefore, they see FeNO levels as a good indicator for prescribing ICS, but not sufficient for ruling out the need for ICS.

The NHLBI guidelines recommend FeNO testing as an adjunct to the evaluation process in individuals for whom the diagnosis of asthma is uncertain. Additionally, they recommend that if FeNO is used, it be part of an ongoing asthma monitoring and management strategy for those with persistent asthma where managing anti-inflammatory therapies is uncertain.

While all discussed guidelines are clear about the benefits of FeNO, ongoing research will continue to provide a fuller understanding of the potential of FeNO in asthma management.

The role of NIOX in the creation of the guidelines

Several clinical studies and technological advancements have made measuring FeNO a lot easier.5 As the use of FeNO testing becomes increasingly common in practice and the evidence base grows, it is likely that guidelines will become more aligned.

Many studies have been carried out and are still ongoing that shed a clearer light on the effect of FeNO measurement in different areas of asthma management. Circassia’s NIOX® devices have been the most widely used for measuring FeNO values in clinical research.6 They have provided an important body of data that has been used in the creation of the various guidelines. They have been proven to show precise and reproducible results and provide a solid base for both research and clinical management of eosinophilic airway inflammation.5

More information about NIOX®

Learn more about Circassia’s NIOX® FeNO testing devices at You can also contact us directly using the contact details / form below:

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1. Dweik RA et al. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FENO) for clinical applications. Am J Respir Crit Care Med. 2011;184(5):602-15.
2. Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention, 2018 Update. 2018.
3. Expert Panel Working Group of the National Heart, Lung, and Blood Institute (NHLBI) administered and coordinated National Asthma Education and Prevention Program Coordinating Committee (NAEPPCC) et al. 2020 Focused Updates to the Asthma Management Guidelines: A Report from the National Asthma Education and Prevention Program Coordinating Committee Expert Panel Working Group. J Allergy Clin Immunol. 2020 Dec;146(6):1217-1270.
4. Karrasch S et al. Accuracy of FENO for diagnosing asthma: a systematic review. Thorax. 2017;72(2):109-116.
5. Alving K et al. Validation of a new portable exhaled nitric oxide analyzer, NIOX VERO®: randomized studies in asthma. Pulm Ther. 2017;3(1):207-218.
6. Data on file. Circassia Ltd. C-NIOX-0006.