Asthma Control Test: Reliability, Validity, and Responsiveness in Patients Not Previously Followed by Asthma Specialists

Abstract

Schatz M, Sorkness CA, Li JT, et al. J Allergy Clin Immunol. 2006;117:549–556

PURPOSE OF THE STUDY. To evaluate the validity and reliability of the asthma-control test (ACT) and assess its responsiveness to changes in asthma control over time in a sample of patients who were new to the care of an asthma specialist.

STUDY POPULATION. Participants were asthmatic subjects (N = 313) aged ≥12 years who had not consulted an asthma specialist within 5 years and had a previous diagnosis of asthma.

METHODS. This prospective trial was conducted in 6 asthma specialty practices. Participants were evaluated at 2 physician office visits (a baseline visit and a follow-up visit separated by 4–12 weeks) in which they completed the ACT, the Asthma Control Questionnaire (ACQ), and prebronchodilator measurements of forced expiratory volume in 1 second (FEV₁). The ACT is a 5-item patient-administered survey for assessing asthma control. Each of the 5 questions is given a score from 1 to 5. Responses from the ACT are summed to yield a score that ranges from 5 (poor control) to 25 (complete control). Asthma specialists, who were blinded to the ACT and ACQ results, rated asthma control on a 5-point Likert scale (not completely controlled to completely controlled) based on history, physical examination, FEV₁ scores, and National Asthma Education and Prevention Program–defined goals for asthma control. Reliability, validity, and responsiveness were all tested via comparison of the ACT results to the specialists’ evaluation, the ACQ scores, and the FEV₁ scores.

RESULTS. Participants (N = 313) had a mean age of 35 years (12–84 years). At baseline, specialists rated asthma control as well controlled or completely controlled (48%), somewhat controlled (29%), and not controlled (23%). The reliability of the ACT was tested by internal consistency and test-retest methods. The internal consistency was .85 for the initial visit (n = 313) and .79 for the follow-up visit (n = 248). The test-retest assessment among 86 patients with the same specialist rating for asthma was .77. The criterion validity was based on comparisons between the ACT scores at the baseline visit and the specialists’ assessment as well as the ACQ scores and FEV₁ values. All of these comparisons were found to be statistically significant. The discriminant validity was measured in 3 ways: the asthma specialists’ rating, percent predicted value of FEV₁, and treatment recommendation of the asthma specialists. As predicted, patients with low ACT scores correlated with diagnoses of poorer control by asthma specialists. Patients with low FEV₁ scores also scored lower on the ACT, and patients who required an increase in their therapy had lower scores on this questionnaire. The responsiveness of the ACT was also measured by assessing the changes in scores between the initial and follow-up visits. Moderate correlations existed between the ACT and the asthma specialist's score, whereas changes in the ACT and ACQ were found to be highly consistent. Changes in FEV₁ and ACT were only minimally correlated. An ACT score of ≤19 identified patients with poorly controlled asthma (71% sensitivity; 71% specificity).

CONCLUSIONS. The ACT was reliable, valid, and responsive to changes in asthma control over time in a sample of patients who were new to the care of an asthma specialist.

REVIEWER COMMENTS. These authors have further shown the value of the ACT in assessing asthma control in the practice of asthma specialists. In a day when physicians are pressed for time when evaluating patients, it is important to find effective tools that are reliable, valid, responsive, and practical to assist in patient evaluations. Additional work is needed to assess the usefulness of the ACT within primary care, where it may prove to be even more valuable in assessing asthma control.