Determination of fractional exhaled nitric oxide (FENO) reference values in healthy Thai population

Fractional exhaled nitric oxide (FENO) level is directly correlated with airway inflammation in asthma patients. The objective of this study was to define normal FENO levels in healthy Thai volunteers.

This prospective cohort study was conducted in healthy Thai volunteers aged ≥5 years. Demographic and clinical data were recorded and pulmonary function test (PFT) was performed. FENO was measured using a chemiluminescence nitric oxide analyzer.

Seventy-nine healthy Thai volunteers with normal lung function test were included. Mean age of participants was 13 (6-47) years and 58.2% were female. All subjects had no history of allergic respiratory diseases. Mean FENO level increased with age, and the differences between age groups were statistically significant (p=0.001). The highest mean FENO level was 13.6 ppb in the 11-15 year age group, and then the FENO level gradually declined with age. The highest mean FENO level was found in the 18-24.9 body mass index (BMI) group. Significant differences were observed for FENO levels between different height groups (p=0.005) but not between different BMI groups (p=0.46). Fair correlations between FENO levels and body weight, height, FEV1, and FVC were observed. A fair correlation between FENO level and age, FENO level and FEF25%-75% was found only in volunteers ≤15 years of age.

FENO level in healthy Thais increased with age until reaching maximum level (mean FENO 13.6 ppb) in the 11-15 year age group. Significant differences were observed for FENO levels between different age groups and different height groups.