Measuring asthma control in group studies: do we need airway calibre and rescue β2-agonist use?

Collection of airway calibre and beta2-agonist data in large clinical trials and epidemiological surveys is sometimes difficult and may be an inefficient use of resources. The aim of this study was to determine whether the omission of the forced expiratory volume in 1 sec (FEV1) and beta2-agonist questions from the seven-item Asthma Control Questionnaire (ACQ) alters its measurement properties and validity. In an observational study, 50 adults with symptomatic asthma attended the clinic at 0, 1, 5 and 9 weeks to complete the ACQ and other measures of asthma status. All patients completed the study and provided complete data sets. Omission of the FEV1 and beta2-agonist questions from the ACQ made minimal difference to the reliability, responsiveness, and both cross-sectional and longitudinal validity of the instrument. Omission of the FEV1 question significantly lowered the summary score (P<0.001) but omission of the beta2-agonist question did not alter it (P>0.05). In group studies, both the FEV1 and beta2-agonist questions may be omitted from the ACQ without changing the validity or the measurement properties of the instrument. Lowering of the summary score by the omission of the FEV1 question means that data from this abbreviated form cannot be combined with or compared to data collected using the full questionnaire.