The fraction of exhaled NO (FeNO) may be a valuable tool for the follow-up of asthmatic patients. However, its usefulness as a screening tool for asthma is not established.
In a study of 961 patients, FeNO values of less than 19 ppb had a 85.2% specificity and 52.4% sensitivity for the diagnosis of asthma. FeNO values of less than 25 ppb were characterized by specificity of less than 90% for the diagnosis of asthma both in smokers and in nonsmokers. FeNO was not a good marker for the differentiation between asthma and allergic rhinitis.
Active and passive smoking decreased FeNO levels in adults.
The current chemiluminescence FeNO analyzers (e.g. NIOX) are costly and lack transportability. Newer hand-held devices are available (NIOX MINO), and according to a recent study, they are just as reliable as their bulkier counterparts. The price of one NIOX MINO unit is around $ 4,200.
NO is synthesized from L-arginine by the enzyme nitric oxide synthase (NOS). Measuring exhaled nitric oxide (FeNO) can serve as a marker of airway inflammation because levels increase in asthma exacerbation and decrease with corticosteroid therapy.
Inflammation in asthma (mind map). FeNO is a marker of oxidative stress. See more Allergy and Immunology mind maps here.
A 2012 study in the journal Thorax showed that tailoring of asthma treatment based on FeNO levels was ineffective in improving outcomes in children and adults.
Portable Exhaled Nitric Oxide as a Screening Tool for Asthma in Young Adults During Pollen Season. Medscape.
Exhaled nitric oxide (FeNO) in asthma and sinusitis
Many atopic diseases increase exhaled nitric oxide (FeNO)
Image source: NioxMino.
Image source: Wikipedia.