Monitoring childhood asthma: Web-based diaries and the asthma control test

Background: Data from asthma diaries are frequently used as an end point in asthma studies; however, data on the validity of Web-based diaries are scarce. Objectives: First, we examined the validity of a Web-based diary in assessing asthma control. Second, we determined the cutoff points for well-controlled asthma of the Childhood Asthma Control Test (C-ACT) and the Asthma Control Test (ACT), and calculated the minimal important difference for both tests. Methods: Children with asthma, ages 4-18 years (n = 228) completed a 4-week Web-based diary, C-ACT, ACT, and an asthma-related quality-of-life questionnaire at baseline and after 1-year follow-up. Results: The completion rate of the Web-based diaries was 89%. The diary scores correlated strongly with C-ACT and ACT scores (r = -0.73, P < .01; r = -0.64, P < .01, respectively) and the changes in diary scores correlated well with changes in C-ACT and ACT scores. The best cutoff points for well-controlled asthma were C-ACT >= 22 and ACT >= 23. The minimal important differences were 1.9 (95% CI, 1.3-2.5) for ACT and 1.6 (95% CI, 1.1-2.1) for C-ACT, and 20.7 points/d (95% CI, -1.1 to -0.4) for the Web-based diary. Conclusions: Our Web-based diary was valid for recording asthma symptoms. Cutoff points of >= 22 (C-ACT) and >= 23 (ACT) define well-controlled asthma. We recommend a 2 C-ACT and ACT points difference as minimally important.