Table 2

 Feno levels as an aid to diagnosis of chronic respiratory symptoms

Feno (ppb)RangeEosinophilic airway inflammationInterpretation (as an aid to diagnosis of chronic respiratory symptoms)
AdultsChildren
5Low (<20 ppb if 12 years or younger; <25 ppb for adults)UnlikelyConsider: Neutrophilic asthma Anxiety/hyperventilation Vocal cord dysfunction Rhinosinusitis Gastro-oesophageal reflux Cardiac diseaseConsider: Wheezy bronchitis Gastro-oesophageal reflux ENT disorders Cystic fibrosis Primary ciliary dyskinesia (FEno <5 ppb), (check nasal NO) Congenital abnormalities, e.g. airway malacia Other immunodeficiencies
10
15
20
25
30 35 40 45IntermediatePresent but mildInterpretation based on clinical presentationInterpretation based on clinical presentation
50 55 60 65 Higher levelsHighSignificantConsider: Atopic asthma if the history is appropriate.If FEV1 <80% predicted, diagnosis of asthma is very likely Eosinophilic bronchitis Churg-Strauss syndrome A positive response to a trial of inhaled or oral steroid is likely. In ex-smokers with COPD this may also be trueIf combined with any objective evidence of reversible airway obstruction, asthma is very likely and a positive response to a trial of inhaled or oral steroids is likely