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FeNO value for diagnosis and control

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FeNO measurement as a component of therapy monitoring for asthma

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FeNO measurement involves measuring a relevant inflammatory marker of the bronchial tubes in exhaled breath. The inflammatory processes in asthma produce nitric oxide (NO) in the mucous membrane of the airways. This can be quantitatively determined as fractional exhaled NO (FeNO) in exhaled air. The higher the NO content, the more severe the inflammation.

Nitric oxide (NO) is a messenger substance that among other places is produced in the respiratory tract. It is also associated with fighting infections and various inflammatory processes. In the lungs, NO is produced by the epithelial cells of the mucous membrane lining the bronchi.

How are the measured values to be interpreted?

The unit of measurement for NO concentration in air is ppb (parts per billion). In healthy adults, the FeNO value is usually below 25 ppb. A FeNO value above 50 ppb indicates an acute allergic inflammatory event in the lungs.

Detailed explanation of asthma values and meaning, on illustration of Vivatmo display, subdivision green, yellow, red

What is the relationship between FeNO levels and bronchial asthma?

Illustration of normal and inflamed lungs in comparison, turquoise, light blue coloured, NO text clarifies inflammation value

Eosinophilic granulocytes are significantly involved in the pathogenesis of bronchial asthma. The degree of inflammation is indicated by NO concentrations measured in exhaled air. Numerous scientific studies have demonstrated the value of FeNO measurement in confirming the diagnosis and predicting the response to inhaled corticosteroids.1-3 According to the Deutsche Atemwegsliga e.V.4, FeNO concentration is therefore a good parameter for determining the extent of eosinophilic airway inflammation in allergic bronchial asthma.5

What do international experts say about FeNO measurement in asthma diagnostics?

In the revised version of the German Asthma Guideline,6 the determination of nitric oxide in breath exhalate (FeNO) is mentioned as part of the initial asthma diagnosis and repeated measurements are recommended.

The American Thoracic Society (ATS) guidelines7 also recommend FeNO measurement for diagnosis, treatment management, and monitoring of asthma patients.

This is supported by a recent English study review8 from 2019/20. This states:

FeNO has also been shown to be a predictive factor for asthma exacerbations, with higher levels associated with a greater number of exacerbations. In addition, higher FeNO levels have been shown to be associated with deteriorating lung function. FeNO testing is a cost-effective procedure and has been shown to improve patient management when combined with standard assessment methods.

The Clinical Guideline on Asthma from the National Institute for Health and Care Excellence (NICE)5 in the United Kingdom also recommends including FeNO measurement in the diagnostic algorithm to improve diagnostic quality and assesses FeNO as a significant parameter for the long-term management of asthma: “Consider using FeNO testing as an option to assist in the asthma management of people who continue to have asthma symptoms despite inhaled corticosteroids.”

1 Dweik et al. Am J Respir Crit Care Med 2011: 184: 602-15
2 Karrasch et al. Thorax 2017; 72:109-16
3 Taylor et al. Thorax 2006; 61: 817-27
4 Deutsche Atemwegsliga e.V. Deutsche Atemwegsliga e.V. in the Deutsche Gesellschaft für Pneumologie
5 Asthma: diagnosis, monitoring and chronic asthma management, NICE guideline, 2017 (Update March 2021)
6 Buhl et al., 2021. Addendum to the German Asthma Guideline.
7 An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications, Dweik et al., 2011 management, Menzies-Gow et al., 2020
8 Menzies-Gow et al Eur Respir J 2020 Mar 26;55(3):1901633