Background: The development of the Asthma Control Test (ACT), a short, simple, patient-based tool for identifying patients with poorly controlled asthma, was recently described in patients under the routine care of an asthma specialist.
Objectives: We sought to evaluate the reliability and validity of the ACT in a longitudinal study of asthmatic patients new to the care of an asthma specialist.
Methods: Patients (n=313) completed the ACT and the Asthma Control Questionnaire (ACQ) at 2 physician visits (4-12 weeks apart). Pulmonary function was measured, and asthma specialists rated asthma control.
Results: Internal consistency reliability of the ACT was 0.85 (baseline) and 0.79 (follow-up). Test-retest reliability was 0.77. Criterion validity was demonstrated by significant correlations between baseline ACT scores and baseline specialists' ratings of asthma control (r=0.52, P<.001) and ACQ scores (r=-0.89, P<.001). Discriminant validity was demonstrated, with significant (P<.001) differences in mean ACT scores across patients differing in asthma control, pulmonary function, and treatment recommendation. Responsiveness of the ACT to changes in asthma control and lung function was demonstrated with significant correlations between changes in ACT scores and changes in specialists' ratings (r=0.44, P<.001), ACQ scores (r=-0.69, P<.001), and percent predicted FEV1 values (r=0.29, P<.001). An ACT score of 19 or less provided optimum balance of sensitivity (71%) and specificity (71%) for detecting uncontrolled asthma.
Conclusions: The ACT is reliable, valid, and responsive to changes in asthma control over time in patients new to the care of asthma specialists. A cutoff score of 19 or less identifies patients with poorly controlled asthma.
Clinical implications: In a clinical setting the ACT should be a useful tool to help physicians identify patients with uncontrolled asthma and facilitate their ability to follow patients' progress with treatment.