Cut-off Points for Defining Asthma Control in Three Versions of the Asthma Control Questionnaire

Introduction: The Asthma Control Questionnaire™ (ACQ) was developed to assess asthma control. The objective of this study is to determine the cut-off points that best differentiate between several types of asthma control in three versions of the ACQ used in clinical practice.

Materials And Methods: It appears 607 adult asthmatic patients (61% female) were recruited from 43 outpatient clinics in Spain. Once the patients were stratified by severity of asthma, they were then evaluated in an epidemiological study. To determine the optimum cut-off points, the area under the receiver operating characteristics (ROC) curve, as well as sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively), was calculated for each version of the ACQ (ACQ-FEV₁ (forced expiratory volume in the first second), ACQ-PEF (peak expiratory flow), and ACQ-wLF (without lung function)).

Results: The optimal cut-off for ACQ-FEV₁ was 1.14 (the sum of 8 points/7 items), for ACQ-PEF 1.28 (the sum of 9 points/7 items), and for ACQ-wLF 0.83 (the sum of 5 points/6 items), and the percentage of correctly classified patients was 76.5%, 77.3%, and 77.2%, respectively. A comparison of ROCs obtained from the three versions of the ACQ shows that ACQ-wLF had a significantly greater area under the curves (AUC) (p = .004) than ACQ-FEV₁. Patients were considered as having some control if their ACQ-FEV₁ score fell between 1.14 and 1.57, if ACQ-PEF values were between 1.28 and 1.57, or if ACQ-wLF scores ranged between 0.83 and 1.5.

Conclusions: Our study, which was carried out in a manner which more closely reflects clinical practice, reveals differences in cut-offs used to define well-controlled asthma among three versions of the ACQ.