What does a single exhaled nitric oxide measurement tell us in asthmatic children?

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.

The aim of this prospective transversal study was to evaluate the relative contributions to exhaled NO fraction (FE(NO)) 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.

FE(NO) 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."

A multivariate analysis of FE(NO) as dependent variable showed that explanatory variables explained 23% of total FE(NO) variance (symptoms > atopy > ICS). In the children without recent symptoms (n = 118), a FE(NO) > 23 ppb predicted atopy (sensitivity 47%, specificity 85%, p = 0.0006). Multiple regression only showed a trend to significance between FE(NO) and the dose of ICS (p = 0.057, r = - 0.19). Incidentally, despite similar dose of ICS, children under fluticasone (mean +/- SD, 259 +/- 149 microg/day) had lower FE(NO) than those under budesonide (299 +/- 195 microg/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 FE(NO) and ARPE index was significant in children with exclusive seasonal sensitisation (n = 31, r = 0.48, p = 0.008).

Common exhaled NO determinants weakly explain a single value of FE(NO), which only can confidently predict atopy.