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.