Prevalence of airway obstruction assessed by lung function questionnaire
OBJECTIVE: To estimate the prevalence of unidentified chronic obstructive pulmonary disease (COPD) and determine the screening accuracy of the Lung Function Questionnaire (LFQ).
PATIENTS AND METHODS: Cigarette smokers who had a smoking history of 10 or more pack-years and were aged 30 years or older were recruited from 36 centers from February 18, 2009, to May 29, 2009. A total of 1575 patients completed a Web-based survey including the 5-item LFQ. Spirometry was performed on patients with an LFQ total score of 18 or less and on a subset scoring more than 18. The primary outcome was the proportion of patients at risk of airflow obstruction as measured by the LFQ (score, ?18) in whom an airflow obstruction was confirmed by spirometry.
RESULTS: Of the patients who completed the LFQ, 849 (54%) had standardized spirometry data available. On the basis of LFQ and spirometry results, the estimated prevalence of possible COPD was 17.9% (95% confidence interval, 15.3%-20.6%). At a cut point of 18 or less, sensitivity, specificity, positive predictive value, and negative predictive value of the LFQ were 88%, 25%, 21%, and 90%, respectively. Approximately 1 in 5 patients (21%) aged 30 years or older and 1 in 4 (26%) aged 50 years or older scored 18 or less on the LFQ and had a ratio of forced expiratory volume in the first second of expiration to forced vital capacity less than 0.70.
CONCLUSION: On the basis of postbronchodilator spirometry results using weighted estimates, approximately 1 in 5 patients (21%) aged 30 years or older with a smoking history of 10 or more pack-years seen in a primary care setting is likely to have COPD. The LFQ could be a helpful COPD case-finding tool for clinicians to identify patients who need further evaluation.