(1) Compare ideal cut-off points for DS and %FEV₁ at 1 and 3 h to predict hospitalization/relapse in subjects with moderate to severe asthma exacerbation (2) Develop a multivariate regression model using DS, %FEV₁, demographic, and clinical variables to predict hospitalization/relapse.

Subjects with acute exacerbation of asthma (FEV₁ <50% predicted following 30 min of standardized treatment: 5 mg nebulized albuterol; 0.5–1.5 mg nebulized ipratropium; and 50 mg oral prednisone) were eligible. All subjects had %FEV₁ and DS obtained at baseline and hourly for 3 h. Using hospitalization/relapse as the outcome of interest; we compared the area under the receiveroperator curves (AUC) between the 1 and 3 h DS and %FEV₁ measurements, and the AUC for the change in DS and %FEV₁ between baseline and hour-3. We determined ideal cut-points for %FEV₁ and DS to maximize sensitivity and specificity. Sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios (LR) were compared between %FEV₁ and DS. We developed a multivariate regression model examining the association of specific demographic and clinical variables to hospitalization/relapse.

142 patients were included for analysis. The AUC was greatest for the 3-h DS (0.721), followed by the 3-h %FEV₁ (0.669). Optimum cut-off values were a DS of 2, and an FEV₁ of 42%. These were associated with a +LR for the composite outcome of 3.06 and 2.48 respectively. Logistic regression showed baseline DS, 3-h DS, change in DS, and oxygen use at hour 3 were all associated with the composite outcome.

The 3-h score for %FEV₁ and DS performed better than scores at any other time point and better than either parameter over time. The 3-h DS had the greatest association with the composite outcome. Neither test was a strong enough predictor to be used solely for this purpose.