Fractional exhaled nitric oxide (FeNO) is used clinically as a biomarker of eosinophilic airway inflammation. Awareness of the factors influencing FeNO values is important for valid clinical interpretation.
We undertook a systematic review of PubMed, Cochrane Library, Scopus and Web of Science databases, as well as reference lists of included articles to evaluate whether ethnicity influences FeNO values, and to determine if this influence affects clinical interpretation according to current guidelines. We included all studies that performed online FeNO measurements on at least 25 healthy, non-Caucasian individuals, and examined the effect of ethnicity on FeNO.
From 62 potential studies, 12 studies were included. One study recruited only children (<12 years), six studies recruited children and/or adolescents, four studies recruited adults only, and a single study involved children, adolescents, and adults. In total, 16 different ethnic populations representing 11 ethnicities were studied. Ethnicity was considered a significant influencing factor in ten of the included studies. We found the geometric mean FeNO to be above the normal healthy range in two studies. We also identified five studies in which at least 5% of participants had FeNO results above the age-specific inflammatory ranges.
Ethnicity influences FeNO values and for some ethnic groups this influence likely affects clinical interpretation according to current guidelines. There is a need to establish healthy FeNO reference ranges for specific ethnic groups in order to improve clinical application.