Background: In epidemiological studies, items about physician-diagnosed COPD are often used. There is a lack of validation and standardization of these items.
Materials and methods: In a general population-based study, 1,050 subjects completed a questionnaire and performed spirometry, including forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) after inhalation of 400 µg of salbutamol. COPD was defined as the ratio of FEV1/FVC <0.7 after bronchodilation. Physician-diagnosed COPD was defined as an affirmative answer to the single item: "Have you ever had COPD diagnosed by a physician?", physician-diagnosed COPD/emphysema as an affirmative answer to any of the two single items; "Have you ever had COPD diagnosed by a physician?" or "Have you ever been told by a physician that you have emphysema?", physician-diagnosed chronic bronchitis as an affirmative answer to; "Have you ever been told by a physician that you have chronic bronchitis?" and physician-diagnosed COPD, emphysema or chronic bronchitis was defined as an affirmative answer to either of the three items above.
Results: For the single item about physician-diagnosed COPD, the sensitivity was around 0.11 and the specificity was almost 0.99 in relation to COPD. The sensitivity of the combined items about COPD/emphysema in detecting COPD was 0.11 and the specificity was high, 0.985. When the items about physician-diagnosed COPD, emphysema or chronic bronchitis were merged as one entity, the sensitivity went up (0.13) and the specificity went down (0.95).
Conclusion: Items about physician-diagnosed COPD have low sensitivity but a very high specificity, indicating that these items will minimize the proportion of false positives. The low sensitivity will underestimate the total burden of COPD in the general population. Items about physician-diagnosed COPD may be used in studies of risk factors for COPD, but are not recommended in prevalence studies.
Keywords: epidemiology; general-population; obstructive lung diseases; questionnaire; validity.