Use of exhaled nitric oxide in the diagnosis and monitoring of childhood asthma: myth or maxim?

Asthma is a common condition in children. This review describes the evidence from the literature and international asthma guidelines for using fractional exhaled nitric oxide (FENO) in the diagnosis and monitoring of childhood asthma. The accuracy of FENO measuring devices could be further improved, the difference in FENO results between devices are equivalent to what is considered a clinically important difference. For diagnosing asthma no guideline currently recommends FENO is used as the first test, but many recommend FENO as part of a series of tests. A cut-off of 35 ppb is widely recommended as being supportive of an asthma diagnosis, but evidence from children at risk of asthma suggests that a lower threshold of 25 ppb may be more appropriate. Nine randomised clinical trials including 1885 children have added FENO to usual asthma care and find that exacerbations are reduced when care is guided by FENO (OR for exacerbation compared to usual care 0.77, 95% CI 0.62-0.94). What is not clear is what cut-off(s) of FENO should be used to trigger a change in treatment. After 30 years of intensive research there is not sufficient evidence to recommend FENO for routine diagnosing and monitoring asthma in children.