Spirometry-adjusted fraction of exhaled nitric oxide increases accuracy for assessment of asthma control in children

Abstract

Spirometry and exhaled nitric oxide are two important complimentary tools to identify and assess asthma control in children. We aimed to determine the ability of a new suggested spirometry-adjusted fraction of exhaled nitric oxide (NO) index in doing that. A random sample of 1602 schoolchildren were screened by a health questionnaire, skin prick tests, spirometry with bronchodilation and exhaled NO. A total of 662 children were included with median (IQR) exhaled NO 11(14) ppb. Receiver operating characteristic (ROC) curves using exhaled NO equations from Malmberg, Kovesi and Buchvald, and spirometry-adjusted fraction of exhaled NO values were applied to identify asthmatic children and uncontrolled asthma. Receiver operating characteristic (ROC) curves failed to identify asthmatic children (all AUC<0.700). Spirometry-adjusted fraction of exhaled NO/FEV1 (AUC=0.712; P=.010) and NO/FEF25%-75% (AUC=0.735 P=.004) had a fair and increased ability to identify uncontrolled disease compared with exhaled NO (AUC=0.707; P=.011) or the Malmberg equation (AUC=0.701; P=.014). Sensitivity and specificity identifying non-controlled asthma were 59% and 81%, respectively, for the cut-off value of 9.7ppb/L for exhaled NO/FEV1, and 40% and 100% for 15.7ppb/L/s for exhaled NO/FEF25%-75%. Exhaled NO did not allow to identify childhood asthma. Spirometry-adjusted fraction of exhaled NO performed better-assessing asthma control in children. Thus, although more validation studies are needed, we suggest its use in epidemiological studies to assess asthma control.