Using fractional exhaled nitric oxide to guide step-down treatment decisions in patients with asthma: a systematic review and individual patient data meta-analysis

BackgroundHigh exhaled nitric oxide fraction (FENO) levels are associated with greater risk of asthma exacerbation. However, it is not clear howFENOcan be used to guide safe reductions in inhaled corticosteroid (ICS) doses in asthma patients. This study assesses the ability ofFENOto guide ICS reductions.MethodsSystematic searching of electronic databases identified prospective observational studies and randomised controlled trials which recruited participants with mild-to-moderate asthma aged ≥12 years and measuredFENObefore reducing ICS. We performed multilevel mixed-effects logistic regression in relation to acute exacerbations and estimated each participant's exacerbation risk using our logistic regression model.ResultsWe included data from seven out of eight eligible studies, representing 384 participants. ICS doses were halved in four studies and withdrawn in three studies. A baselineFENOmeasurement of ≥50 ppb was associated with increased risk of exacerbations (crude OR 3.14, 95% CI 1.41–7.00, p=0.005; adjusted OR 3.08, 95% CI 1.36–6.98, p=0.007) and corresponded to an estimated exacerbation risk cut-off of 15%. Reducing ICS when estimated exacerbation risk was <15%versus<10% would result in fewer patients remaining on the same ICS dose (40 (10.4%) out of 384versus141 (36.7%) out of 384), but similar proportions of patients avoiding exacerbations (222 (91.4%) out of 243, 95% CI 87.1–94.6%versus311 (90.4%) out of 344, 95% CI 86.8–93.3%).ConclusionIn patients with mild-to-moderate asthma, gradual ICS reduction whenFENOis <50 ppb may help decrease ICS use without increasing exacerbations. Future research should aim to validate these findings in larger populations.