A summary of the recommended FENO cut-off values for use in asthma diagnosis and management from international guidelines
| Age range for children years | Healthy values ppb | Intermediate values ppb | Elevated values ppb | Recommended role of FENO in diagnosing asthma | Recommended role of FENO in diagnosing asthma | ||||
| Children | Adults | Children | Adults | Children | Adults | ||||
| ATS (2011) [2] | <12 | <20 | <25 | 20–35 | 25–50 | >35 | >50 | FENO may be used to support the diagnosis of asthma in situations in which objective evidence is needed. | The use of FENO in monitoring airway inflammation in patients with asthma is recommended |
| National Institute for Health and Care Excellence (2017) [9] | 5–16 | Not stated | Not stated | Not stated | Not stated | >35 | >40 | Diagnose asthma if patients have symptoms suggestive of asthma, an elevated FENO, positive peak flow variability or obstructive spirometry, and positive bronchodilator reversibility | Do not routinely use FENO use to monitor asthma control |
| GINA (2019) [11] | 6–11 | Not stated | Not stated | Not stated | Not stated | >50 | >50 | FENO has not been established for ruling in or ruling out a diagnosis of asthma | FENO-guided treatment is not recommended for the general population There may be a role for FENO in a severe asthma clinic; cut-offs of 20, 25 and 50 ppb may have a role in stratifying treatment |
| British Thoracic Society/Scottish Intercollegiate Guidelines (2019) [12] | 5–16 | >35 | >40 | Use measurement of FENO (if available) to find evidence of eosinophilic inflammation A positive test increases the probability of asthma but a negative test does not exclude asthma | Except in specialist asthma clinics, the routine use of FENO testing to monitor asthma in adults or children is not recommended | ||||