Forced expiratory volume in 1 second percentage improves the classification of severity among children with asthma

OBJECTIVE. Spirometry is an important component of the National Asthma Education and Prevention Program guidelines for asthma, yet published data show variable associations between forced expiratory volume in 1 second percentage (FEV₁%) predicted, symptoms and health care utilization. The objective of this analysis was to examine the association between FEV ₁% and future risk of exacerbations among a well-characterized population of children with asthma. METHODS. Using data that are available from the Childhood Asthma Management Program, we examined the relationship between prebronchodilator FEV₁% and important clinical outcomes. Multiple observations of FEV₁ were available for each patient; multivariate regression analysis, using a general estimating equation approach, was used to control for the correlation between repeated measurements among individuals and potential confounders. FEV₁% was categorized into 4 levels and as a continuous variable. Outcomes of interest included mean symptom score (0-3), episode-free days, and asthma-related events (oral steroid use, emergency department visits, and hospitalizations) during the ensuing 4-month period. Our analysis was limited to the placebo group (N = 417). RESULTS. We observed a clear relationship between prebronchodilator FEV₁% and important clinical outcomes. In multivariable models that simultaneously controlled for covariates of interest, age at baseline, time, previous event history, and nocturnal awakenings, a significant relationship between FEV₁% and asthma symptoms and serious asthma exacerbations (oral steroids, emergency department visits, and hospitalizations) was observed. Compared with children with an FEV₁% ≥100%, children with FEV₁% 80% to 99%, 60% to 79%, and <60% were 1.3, 1.8, and 4.8, respectively, more likely to have a serious asthma exacerbation during the ensuing 4 months. CONCLUSIONS. In children with mild to moderate asthma, FEV₁% predicted is independently associated with future asthma symptoms and health care utilization. Previous asthma-related hospitalizations and nocturnal symptoms also were independently associated with risk for future adverse events. FEV ₁ is an important component of asthma health status and asthma severity classification.