Exhaled Nitric Oxide May Help Screen for Asthma in Young Adults

October 31, 2007 — The fraction of exhaled nitric oxide (FeNO) measurement with a portable analyzer is an effective tool to screen for asthma in young adults, according to the results of a study reported in the October 20 Online First issue of Chest.
"The fraction of exhaled NO (FeNO) is valuable for the follow-up of asthmatic patients," write Konstantinos Kostikas, MD, from the University of Thessaly Medical School, University Hospital of Larissa, in Greece, and colleagues. "However, its usefulness as a screening tool for asthma is not established."
Using a modified European Community Respiratory Health Survey (ECRHS) questionnaire previously developed to screen respiratory tract symptoms related to asthma, the investigators screened a population of 961 university students.
There were 149 students with a positive answer to at least 1 question on the ECRHS; these underwent FeNO measurement with a portable nitric oxide (NO) analyzer followed by spirometry, which was evaluated by a physician blinded to FeNO measurements. Controls were 70 students with no respiratory tract symptoms.
Asthma was diagnosed in 63 students and allergic rhinitis in 57 students. Compared with controls, patients with asthma had higher FeNO (median, 20; interquartile range, 14 - 31 ppb vs 11 [7 - 13] ppb; P < .0001). However, their FeNO values were not significantly higher vs patients with allergic rhinitis (17 [12 - 23] ppb; P = .28).
For the diagnosis of asthma, FeNO cutoff values of more than 19 ppb had a specificity of 85.2% and sensitivity of 52.4% (area under the curve [AUC] = 0.723). In nonsmokers, the diagnostic performance of FeNO was better (AUC = 0.805). Both in smokers and in nonsmokers, FeNO values greater than 25 ppb were more than 90% specific for the diagnosis of asthma. However, FeNO was not a good marker to distinguish asthma from allergic rhinitis.
Limitations of the study are that FeNO represents a marker of eosinophilic airway inflammation and is not elevated in noneosinophilic asthma, use of physician-diagnosed asthma as the criterion standard study group is limited to young adults, and most patients had mild to moderate asthma.
"FeNO measurement with a portable analyzer is useful for the screening for asthma in young adults," the study authors write. "Significant confounding factors are allergic rhinitis and current smoking. In the era of wider availability and lowering cost of FeNO analyzers, further studies in other age groups are warranted for its validation as a screening tool for asthma in the general population."