BACKGROUND: Repeated measurements of spirometry and fractional exhaled nitric oxide (FENO) are recommended as part of the management of childhood asthma, but the evidence base for such recommendations is small. We tested the hypothesis that reducing spirometric indices or increasing FENO will predict poor future asthma outcomes.METHODS: A one-stage individual patient data meta-analysis used data from seven randomized controlled trials in which FENO was used to guide asthma treatment; spirometric indices were also measured. Change in %FEV 1 and % change in FENO between baseline and 3 months were related to having poor asthma control and to having an asthma exacerbation between 3 and 6 months after baseline.RESULTS: Data were available from 1,112 children (mean age, 12.6 years; mean %FEV 1 , 94%). A 10% reduction in %FEV 1 between baseline and 3 months was associated with 28% increased odds for asthma exacerbation (95% CI, 3-58) and with 21% increased odds for having poor asthma control (95% CI, 0-45) 6 months after baseline. A 50% increase in FENO between baseline and 3 months was associated with 11% increase in odds for poor asthma control 6 months after baseline (95% CI, 0-16). Baseline FENO and %FEV 1 were not related to asthma outcomes at 3 months.CONCLUSIONS: Repeated measurements of %FEV 1 that are typically within the "normal" range add to clinical risk assessment of future asthma outcomes in children. The role of repeated FENO measurements is less certain because large changes were associated with small changes in outcome risk.