Background: The COPD Diagnostic Questionnaire (CDQ) was developed to identify people who would benefit from spirometry testing to confirm Chronic Obstructive Pulmonary Disease (COPD). The aim of this study was to determine the usefulness of a cut-off score of 16.5 on the CDQ in identifying those at increased risk of obstruction, in a mixed population of people 'at risk'of COPD and those with an 'existing' COPD diagnosis.
Methods: People 'at risk' of COPD (aged > 40 years, current/ex-smoker) and those with 'existing' COPD were identified from four general practices and invited to participate. Participants completed the CDQ and those with a CDQ score >= 16.5 were categorised as having intermediate to increased likelihood of airflow obstruction. Pre and post-bronchodilator spirometry determined the presence of airway obstruction (FEV1/FVC ratio < 0.7). Sensitivity, specificity and accuracy of the CDQ was determined compared to spirometry as the gold standard.
Results: One hundred forty-one participants attended an initial assessment ('at risk'= 111 (79%)/existing' COPD = 30 (21%)). A cut-off score of 16.5 corresponded to a sensitivity of 81%, specificity of 36% and accuracy of 50%, in the entire mixed population. The area under the ROC curve was 0.59 +/- 0.50 indicating low diagnostic accuracy of the CDQ. Similar results were found in the 'existing' COPD group alone.
Conclusion: Whilst a cut-off score of 16.5 on the CDQ may result in a large number of false positives, clinicians may still wish to use the CDQ to refine who receives spirometry due to its high sensitivity.