Measuring asthma control in group studies: do we need airway calibre and rescue beta(2)-agonist use?

Collection of airway calibre and pl-agonist data in large clinical trials a nd epidemiological surveys is sometimes difficult and may be an inefficient use of resources. The aim of this study was to determine whether the omiss ion of the forced expiratory volume in 1 sec (FEV1) and beta (2)-agonist qu estions from the seven-item Asthma Control Questionnaire (ACQ) alters its m easurement properties and validity. In an observational study, 50 adults with symptomatic asthma attended the c linic at 0, 1, 5 and 9 weeks to complete the ACQ and other measures of asth ma status. All patients completed the study and provided complete data sets. Omission of the FEV1 and beta (1)-agonist questions from the ACQ made minimal differ ence to the reliability, responsiveness, and both cross-sectional and longi tudinal validity of the instrument. Omission of the FEV1 question significa ntly lowered the summary score (P < 0.0001) but omission of the beta (2)-ag onist question did not alter it (P > 0.05). In group studies, both the FEV1 and beta (2)-agonist questions may be omitt ed from the ACQ without changing the validity or the measurement properties of the instrument. Lowering of the summary score by the omission of the FE V1 question means that data from this abbreviated form cannot be combined w ith or compared to data collected using the full questionnaire.