Clinical Edge

Summaries of Must-Read Clinical Literature, Guidelines, and FDA Actions

Fractional Exhaled Nitric Oxide Testing in Asthma

Mayo Clin Proc; ePub 2017 Dec 20; Wang, et al

In individuals aged ≥5 years, fractional exhaled nitric oxide (FeNO) measurement has only moderate accuracy to diagnose asthma, a recent study found. The systematic review and meta-analyses included 43 studies and a total of 13,747 patients. Researchers found:

  • In adults, using FeNO cutoffs <20, 20 to 29, 30 to 39, and ≥40 parts per billion, FeNO testing had sensitivities of 0.80, 0.69, 0.53, and 0.41, respectively, and specificities of 0.64, 0.78, 0.85, and 0.93, respectively.
  • In children, using FeNO cutoffs of <20, and 20 to 29 parts per billion, FeNO testing displayed sensitivities of 0.78 and 0.61, respectively, and specificities of 0.79 and 0.89, respectively.
  • The posttest odds of having asthma with a positive FeNO test result increased by 2.80- to 7.00-fold depending on the FeNO cutoff.


Wang Z, Pianosi PT, Keogh KA, et al. The diagnostic accuracy of fractional exhaled nitric oxide testing in asthma: A systematic review and meta-analyses. [Published online ahead of print December 20, 2017]. Mayo Clin Proc. doi:10.1016/j.mayocp.2017.11.012.


Asthma is common, affecting almost twenty-four million Americans. Usually the diagnosis is easy—we hear wheezing on exam that is relieved with a bronchodilator, or a history of intermittent wheezing. Sometimes, though, making a diagnosis can be challenging. This is where a new test, the fractional exhaled nitric oxide (FeNO), may be helpful. Typically diagnosis can be challenging when a patient does not have symptoms in the office but appears to have intermittent bronchospasm as an outpatient and may have a competing diagnosis such as vocal cord dysfunction, GERD with aspiration, or recurrent bronchitis. When this is the case, additional insight into making a diagnosis may be helpful. Asthma is characterized by airway inflammation. Nitrous Oxide (NO) is released from the epithelial cells of the airway during inflammation. The concentration of NO, termed the fractional exhaled nitric oxide (FeNO), is related to airway inflammation, as well as to eosinophilic airway inflammation which is related to the response of asthma to inhaled corticosteroids. Patients with asthma have high FeNO in their exhaled breath and the FeNO decreases in response to inhaled corticosteroid treatment. The current study supports the recommendations of the American Thoracic Society Guidelines on the use of FeNO, which states that, “FENO may be used to support the diagnosis of asthma in situations in which objective evidence is needed”.1Neil Skolnik, MD

  1. Dweik RA, Boggs PB, Erzurum SC, et al. An official ATS clinical practice guideline: Interpretation of exhaled nitric oxide levels (FeNO) for Clinical Applications. American Journal of Respiratory and Critical Care Medicine. 2011;184(5):602-615. doi:10.1164/rccm.9120-11ST.