Table 1

A summary of the recommended FENO cut-off values for use in asthma diagnosis and management from international guidelines

Age range for children yearsHealthy values ppbIntermediate values ppbElevated values ppbRecommended role of FENO in diagnosing asthmaRecommended role of FENO in diagnosing asthma
ATS (2011) [2]<12<20<2520–3525–50>35>50FENO 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]5–16Not statedNot statedNot statedNot stated>35>40Diagnose asthma if patients have symptoms suggestive of asthma, an elevated FENO, positive peak flow variability or obstructive spirometry, and positive bronchodilator reversibilityDo not routinely use FENO use to monitor asthma control
GINA (2019) [11]6–11Not statedNot statedNot statedNot stated>50>50FENO has not been established for ruling in or ruling out a diagnosis of asthmaFENO-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>40Use 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