What is fractional exhaled nitric oxide (FENO) in pulmonary function testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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Measurement of fractional exhaled nitric oxide (FENO) is a noninvasive, safe, and simple method of quantifying airway inflammation. FENO in asthma may have the utility of helping make the diagnosis, monitoring the patient's compliance with prescribed medications, and predicting pending exacerbations.

It is important to recognize that asthma is a clinical diagnosis and FENO is not diagnostic for asthma, nor does a normal FENO measurement not exclude the diagnosis of asthma. FENO may be low in asthma not due to airway eosinophilia. FENO does have utility in predicting steroid responsiveness, even in the absence of induced sputum eosinophils.

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