Validation of a guideline-based composite outcome assessment tool for asthma control

BACKGROUND A global definition of asthma control does not currently exist. The purpose of this study was to validate two new guideline-based composite measures of asthma control, defined as totally controlled (TC) asthma and well controlled (WC) asthma. METHODS We used data from 3416 patients randomised and treated in the multi-centre Gaining Optimal Asthma controL (GOAL) study. The criteria comprising the asthma control measures were based on Global Initiative for Asthma/National Institutes of Health guidelines. This validation study examined the measurement properties of the asthma control measures using data from run-in, baseline, 12 and 52 weeks. Forced expiratory volume in 1 second (FEV1) and the Asthma Quality of Life Questionnaire (AQLQ) were used as the reference criteria in the validation analysis. RESULTS Both measures had good discriminative ability showing significant differences in FEV1 and AQLQ scores between control classification both cross-sectionally and longitudinally (p < 0.001). Overall both of the composite measures accounted for more of the variance in FEV1 after 52 weeks than the individual components of each asthma control measure. Both of the reference criteria were independently related to each asthma control measure (p < 0.0001). The measures also had good predictive validity showing significant differences in FEV1 and AQLQ scores at 52 weeks by control classification at 12 weeks (p < 0.0001). CONCLUSION The guideline-based composite asthma control measures of WC asthma and TC asthma have good psychometric properties and are both valid functional indices of disease control in asthma.