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 9.7 ppb/L for exhaled NO/FEV1 , and 40% and 100% for 15.7 ppb/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. ; Health, Comfort and Energy in the Built Environment (HEBE), Grant/Award Number: NORTE-01-0145-FEDER-000010; Programa Operacional Regional do Norte, Grant/Award Number: NORTE2020; Fundo Europeu de Desenvolvimento Regional (FEDER); Foundation for Science and Technology schoolarships, Grant/Award Number: SFRH/BD/108605/2015 and SFRH/BD/112269/2015
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