Thorax 61:817-827 doi:10.1136/thx.2005.056093
  • Occasional review

Exhaled nitric oxide measurements: clinical application and interpretation

  1. D R Taylor1,
  2. M W Pijnenburg2,
  3. A D Smith1,
  4. J C D Jongste2
  1. 1Department of Medical and Surgical Sciences, Dunedin School of Medicine, University of Otago, P O Box 913, Dunedin, New Zealand
  2. 2Department of Paediatric Respiratory Medicine, Erasmus MC - Sophia Children’s Hospital, University Medical Centre, P O Box 2060, 3000 CB Rotterdam, The Netherlands
  1. Correspondence to:
    Professor D R Taylor
    Department of Medical and Surgical Sciences, Dunedin School of Medicine, University of Otago, P O Box 913, Dunedin, New Zealand; robin.taylor{at}
  • Received 22 November 2005
  • Accepted 7 February 2006


The use of exhaled nitric oxide measurements (FEno) in clinical practice is now coming of age. There are a number of theoretical and practical factors which have brought this about. Firstly, FEno is a good surrogate marker for eosinophilic airway inflammation. High FEno levels may be used to distinguish eosinophilic from non-eosinophilic pathologies. This information complements conventional pulmonary function testing in the assessment of patients with non-specific respiratory symptoms. Secondly, eosinophilic airway inflammation is steroid responsive. There are now sufficient data to justify the claim that FEno measurements may be used successfully to identify and monitor steroid response as well as steroid requirements in the diagnosis and management of airways disease. FEno measurements are also helpful in identifying patients who do/do not require ongoing treatment with inhaled steroids. Thirdly, portable nitric oxide analysers are now available, making routine testing a practical possibility. However, a number of issues still need to be resolved, including the diagnostic role of FEno in preschool children and the use of reference values versus individual FEno profiles in managing patients with difficult or severe asthma.


  • Competing interests: Professor Taylor has received funding from Aerocrine, a manufacturer of nitric oxide analysers.

  • Note: Unless otherwise stated, all FEno measurements are reported in parts per billion at a flow rate of 50 ml/s. In some instances corrections for flow rate have been made to ensure consistency and permit appropriate interpretation by the reader.