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Abstract
Background. Due to the multiple factors affecting exhaled nitric oxide (NO) value, physicians are often puzzled by the result of a single measurement in asthmatic patients. Objective. The aim of this prospective transversal study was to evaluate the relative contributions to exhaled NO fraction (FENO) of the commonly considered major NO determinants, i.e., recent symptoms (upper and lower respiratory tract), atopy (prick skin tests and degree of allergic exposure), and treatment (dose of inhaled corticosteroid [ICS]) to know what information gives a single measure. Methods. FENO at 50 mL/s expiratory flow was measured in 199 asthmatic children (141 boys, age: 11.2 years ± 2.5 years). The allergic risk due to pollen exposure (ARPE index) was independently evaluated by the “Réseau National de Surveillance Aérobiologique.” Results. A multivariate analysis of FENO as dependent variable showed that explanatory variables explained 23% of total FENO variance (symptoms > atopy > ICS). In the children without recent symptoms (n = 118), a FENO > 23 ppb predicted atopy (sensitivity 47%, specificity 85%, p = 0.0006). Multiple regression only showed a trend to significance between FENO and the dose of ICS (p = 0.057, r = − 0.19). Incidentally, despite similar dose of ICS, children under fluticasone (mean ± SD, 259 ± 149 μg/day) had lower FENO than those under budesonide (299 ± 195 μg/day) (median [interquartile], 21 ppb [14–42], n = 55 versus 35 ppb [19–47], n = 104; p = 0.007), which may be due to a higher potency of fluticasone. A relationship between FENO and ARPE index was significant in children with exclusive seasonal sensitisation (n = 31, r = 0.48, p = 0.008). Conclusion. Common exhaled NO determinants weakly explain a single value of FENO, which only can confidently predict atopy.