Validity of a questionnaire-based diagnosis of chronic obstructive pulmonary disease in a general population-based study

BACKGROUND The diagnosis of chronic obstructive pulmonary disease (COPD) is based on airflow obstruction. In epidemiological studies, spirometric data have often been lacking and researchers have had to rely almost solely on questionnaire answers. The aim of this study is to assess the diagnostic accuracy of questionnaire answers to detect COPD. METHODS A sample of the Swedish general population without physician-diagnosed asthma was randomly selected and interviewed using a respiratory questionnaire. All eligible subjects aged 25-75 years (n = 3892) performed spirometry for detection of airflow obstruction using Global Initiative for Chronic Obstructive Lung Disease (GOLD) or American Thoracic Society (ATS)/European Respiratory Society (ERS) criteria. Sensitivity, specificity, positive likelihood ratio (LR+), positive predictive values (PPVs), and negative predictive values (NPVs) were calculated to define diagnostic accuracy of questionnaire answers. RESULTS The sensitivity of the question "Have you been diagnosed by a physician as having COPD or emphysema?" in detecting airflow obstruction was 5.7% using GOLD, and 9.8% using ATS/ERS, criteria; specificity was 99.7% for GOLD and 99.5% for ATS/ERS. Sensitivity, specificity, and PPV were higher for the question compared to self-reported symptoms of chronic bronchitis in identifying subjects with airflow obstruction. CONCLUSIONS The high specificity and good PPV suggest that the question "Have you been diagnosed by a physician as having COPD or emphysema?" is more likely to identify those who do not have airflow obstruction, whereas the low sensitivity of this question could underestimate the real burden of COPD in the general population.