According to national asthma guidelines, asthma severity can be classified as intermittent, mild, moderate, or severe on the basis of lung function, symptoms, nighttime awakenings, and exacerbations. Although it is widely believed that patients might not remain consistently in any given severity category over time, few studies have examined this directly.

We sought to assess the variability in disease severity-control among patients with persistent asthma who have not yet received an asthma maintenance treatment.

We performed an analysis of asthma severity-control over time in placebo-treated patients (n = 85) from 2 randomized, double-blind, 12-week clinical trials in patients with asthma previously receiving β₂-agonists alone. Asthma severity-control was assessed on the basis of morning percent predicted peak expiratory flow, albuterol use, and symptoms.

At baseline, all patients met the criteria for moderate or severe persistent asthma (mean FEV₁ of 64% of predicted value or albuterol use and symptoms on 4.7 and 6.0 days per week, respectively). The mean percentage of treatment weeks that patients met all criteria for intermittent, mild, moderate, and severe asthma were 9%, 14%, 71%, and 6%, respectively. On the basis of morning peak expiratory flow, patients were classified as having intermittent-mild, moderate, or severe disease on 52%, 41%, and 7% of days, respectively. With regard to days per week with albuterol use or asthma symptoms, patients spent 59% and 45% of weeks, respectively, in the intermittent and mild categories.

Asthma control cannot be adequately assessed in many patients by using discrete point-in-time assessments of lung function, short-acting β-agonist use, or asthma symptoms. This might lead to underestimation of disease severity and contribute to inadequate therapy and, ultimately, asthma morbidity.