What Magnitude of Change in FEV 1 is Associated With Increased Odds for Asthma Exacerbation and Loss of Control?

ABSTRACT Background Spirometry (FEV 1 ) is often measured as part of ongoing asthma management, but little is understood about what merits a clinically meaningful change in FEV 1 . Metholology Data were collated from five clinical trials where FEV 1 was measured at 3‐month intervals. Change in FEV 1 over 3‐months was expressed as: FEV 1 change score (Zc), absolute change in %FEV 1 (∆FEV 1 %) and absolute change in FEV 1 z score (∆FEV 1 z). The association between change in FEV 1 over 3 months and asthma outcomes in the following 3 months was estimated using logistic regression. Results Data from 1264 children were analysed. Declines in in Zc between 1.1 and 2.9, in ∆FEV 1 % between 12% and 23% and in ∆FEV 1 z between 0.9 and 2.0, were associated with increased odds ratio (OR) for later asthma exacerbation of between 1.3 and 2.3. Unexpectedly, rises in Zc of 1.7‐1.9 and in ∆FEV 1 % of 14 and 18 were also associated with increased OR for a future exacerbation of between 1.3 and 1.6. Among children with controlled asthma symptoms, declines in Zc of 1.7, in ∆FEV 1 % of 11 and 14 and in ∆FEV 1 z of 0.8‐1.1 were associated with increases in OR for future loss of control of between 1.5 and 1.7. Rises in all three indices of change in FEV 1 were associated with reduced OR between 0.4 and 0.7 for future loss of control. A lower initial FEV 1 z score was associated with higher variability in longitudinal FEV 1 z‐score measurements. Conclusions FEV 1 variability, and not simply a fall in FEV 1 , identifies children at increased risk for future asthma exacerbations. The clinical relevance of a single FEV 1 may be uncertain.