Fractional exhaled nitric oxide in asthma

NICE have stated that (1):

• fractional exhaled nitric oxide (FeNO) testing is recommended as an option to help diagnose asthma in adults and children:
  • in individuals aged 16 or over and suspected of having asthma then blood eosinophil count or fractional exhaled nitric oxide (FeNO) level is the initial diagnostic step
    • asthma is diagnosed if the FeNO level is 50 ppb or more or the eosinophil count is raised
  • in children aged 5 to 16 years old and suspected of having asthma then the initial diagnostic step is measurement of FeNO and asthma is diagnosed if the FeNO level is 35 ppb or more
• be aware that the results of spirometry and FeNO tests may be affected in people who have been treated with inhaled corticosteroids (the test results are more likely to be normal)
• consider fractional exhaled nitric oxide (FeNO) monitoring for adults with asthma:
  • at their regular review, and
  • before and after changing their asthma therapy
• if possible, check the fractional exhaled nitric oxide (FeNO) level when asthma is uncontrolled
  • if it is raised this may indicate poor adherence to treatment or the need for an increased dose of inhaled corticosteroid (ICS)
    • for people aged 12 and over with asthma that is not controlled on moderate-dose MART despite good adherence:
      • it is suggested to check the fractional exhaled nitric oxide (FeNO) level if available, and the blood eosinophil count
        • if either of these is raised, refer to a specialist in asthma care

Notes:

• nitric oxide, which is produced in the lungs and is present in exhaled breath, has been implicated in the pathophysiology of lung diseases, including asthma. It has been shown to act as a vasodilator, bronchodilator, neurotransmitter and inflammatory mediator in the lungs and airways
  
  
• FENO is a marker of asthma, and high levels correlate with ongoing eosinophilic inflammation (2)
  
  
• FENO levels typically come down with inhaled corticosteroids (ICS) in a dose-dependent manner (3)
  
  
• in case of loss of asthma control, FENO increases (4), and there are data to suggest that serial monitoring of FENO can help in titrating corticosteroid doses (5) and predicting exacerbation (6)
  
  
• American Thoracic Society guidelines recommend the use of exhaled NO in management of asthmatics, especially in asthma with eosinophilic inflammation and in predicting response to corticosteroids

Reference:

• 1) NICE (November 2024). Asthma: diagnosis, monitoring and chronic asthma management (BTS, NICE, SIGN)
• 2) Jatakanon A et al. Correlation between exhaled nitric oxide, sputum eosinophils, and methacholine responsiveness in patients with mild asthma. Thorax. 1998;53:91-5.
• 3) Kharitonov SA et al. Dose-dependent onset and cessation of action of inhaled budesonide on exhaled nitric oxide and symptoms in mild asthma. Thorax. 2002;57:889-96.
• 4) Jones SL et al. The predictive value of exhaled nitric oxide measurements in assessing changes in asthma control. Am J Respir Crit Care Med. 2001;164:738-43.
• 5) Pijnenburg MW et al. Titrating steroids on exhaled nitric oxide in children with asthma: a randomized controlled trial. Am J Respir Crit Care Med. 2005;172:831-6.
• 6) Gelb AF et al. Role of spirometry and exhaled nitric oxide to predict exacerbations in treated asthmatics. Chest. 2006; 129:1492-9
• 7) Dweik RA et all. American Thoracic Society Committee on Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FENO) for clinical applications. Am J Respir Crit Care Med. 2011;184:602-15.