Feno levels as an aid to diagnosis of chronic respiratory symptoms
| Feno (ppb) | Range | Eosinophilic airway inflammation | Interpretation (as an aid to diagnosis of chronic respiratory symptoms) | |
|---|---|---|---|---|
| Adults | Children | |||
| 5 | Low (<20 ppb if 12 years or younger; <25 ppb for adults) | Unlikely | Consider: Neutrophilic asthma Anxiety/hyperventilation Vocal cord dysfunction Rhinosinusitis Gastro-oesophageal reflux Cardiac disease | Consider: 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 45 | Intermediate | Present but mild | Interpretation based on clinical presentation | Interpretation based on clinical presentation |
| 50 55 60 65 Higher levels | High | Significant | Consider: 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 true | If 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 |