What Magnitude of Change in FEV₁ is Associated With Increased Odds for Asthma Exacerbation and Loss of Control?

Spirometry (FEV₁) is often measured as part of ongoing asthma management, but little is understood about what merits a clinically meaningful change in FEV₁.

Data were collated from five clinical trials where FEV₁ was measured at 3-month intervals. Change in FEV₁ over 3-months was expressed as: FEV₁ change score (Zc), absolute change in %FEV₁ (∆FEV₁%) and absolute change in FEV₁ z score (∆FEV₁z). The association between change in FEV₁ over 3 months and asthma outcomes in the following 3 months was estimated using logistic regression.

Data from 1264 children were analysed. Declines in in Zc between 1.1 and 2.9, in ∆FEV₁% between 12% and 23% and in ∆FEV₁z 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 ∆FEV₁% 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 ∆FEV₁% of 11 and 14 and in ∆FEV₁z 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 FEV₁ were associated with reduced OR between 0.4 and 0.7 for future loss of control. A lower initial FEV₁ z score was associated with higher variability in longitudinal FEV₁ z-score measurements.

FEV₁ variability, and not simply a fall in FEV₁, identifies children at increased risk for future asthma exacerbations. The clinical relevance of a single FEV₁ may be uncertain.