Validation of a diagnosis-agnostic symptom questionnaire for asthma and/or COPD

BACKGROUND: The Respiratory Symptoms Questionnaire (RSQ) is a novel, four-item patient-reported diagnosis-agnostic tool designed to assess the frequency of respiratory symptoms and their impact on activity, without specifying a particular diagnosis. Our objective was to examine its validity in patients with asthma and/or chronic obstructive pulmonary disease (COPD). METHODS: Baseline data were randomly sampled from patients who completed the RSQ in the NOVELTY study (ClinicalTrials.gov: NCT02760329). The total sample (n=1530) comprised three randomly selected samples (n=510 each) from each physician-assigned diagnostic group (asthma, asthma+COPD and COPD). The internal consistency and structural validity of the RSQ were evaluated using exploratory and confirmatory factor analyses; psychometric performance was observed using Classical Test Theory and Item Response Theory analyses. RESULTS: For the total sample, the mean±sd RSQ score was 5.6±4.3 (range 0–16). Irrespective of diagnosis, the internal consistency of items was uniformly adequate (Cronbach's α=0.76–0.80). All items had high factor loadings and structural characteristics of the measure were invariant across groups. Using the total sample, RSQ items informatively covered the θ score range of –2.0 to 2.8, with discrimination coefficients for individual items being high to very high (1.7–2.6). Strong convergent correlations were observed between the RSQ and the St George's Respiratory Questionnaire (0.77, p<0.001). CONCLUSIONS: The RSQ is a valid, brief, patient-reported tool for assessing respiratory symptoms in patients across the whole spectrum of asthma and/or COPD, rather than using different questionnaires for each diagnosis. It can be used for monitoring respiratory symptoms in clinical practice, clinical trials and real-world studies.