Feasibility of FnNO measurement in preschoolers and development of predictive models

Fractional nasal exhaled nitric oxide (FnNO) is a valuable biomarker of upper airway mucosal inflammation, but its clinical application in preschoolers is limited by uncertain compliance and a lack of reference data. This study aimed to evaluate the feasibility of standardized FnNO measurement in children aged 3-6 years, identify independent predictors of test cooperation and first-attempt success to build exploratory predictive models, and provide preliminary distribution estimates of FnNO in healthy preschoolers.

A total of 148 preschoolers aged 3-6 years were enrolled. Test completion and first-attempt success rates were recorded. Multivariable logistic regression was used to identify independent predictors of compliance. Exploratory predictive models were developed and evaluated using receiver operating characteristic (ROC) analysis with internal bootstrap validation. FnNO distribution characteristics were analyzed in both the general cohort and a healthy subgroup.

The overall test completion rate was 82.4% (122/148), and the first-attempt success rate was 76.2% (77/101). Multivariable analysis demonstrated that female sex (OR = 4.853, P = 0.004) and greater height (OR = 1.216, P = 0.000) were independent predictors of test completion. Age was the sole independent predictor of first-attempt success (OR = 2.299, P = 0.001). The predictive model for test completion (sex and height) achieved an area under the curve (AUC) of 0.870, while the first-attempt success model (age and BMI) yielded an AUC of 0.749. The median FnNO level was 315.50 ppb (IQR: 168.00-410.00 ppb) across the overall cohort and 324.00 ppb (IQR: 221.00-378.50 ppb) in the healthy subgroup (n = 81).

Standardized FnNO measurement is feasible in preschool children. Height, sex, and age are key factors influencing test cooperation. The proposed predictive models offer exploratory statistical tools for population stratification in research contexts, though prospective clinical validation remains necessary. This study establishes preliminary reference estimates for FnNO in Chinese preschoolers.