Rationale: During 2007-2010, the National Health and Nutrition Examination Survey (NHANES), a nationally representative survey of the non-institutionalized US population, conducted a spirometry component which obtained pre-bronchodilator pulmonary lung function data on survey participants 6-79 years of age and post-bronchodilator pulmonary lung function data for the subset of this group with airflow limitation. Data on respiratory symptoms and other respiratory related data were also collected. These data offered a unique opportunity to examine multiple approaches to estimating the prevalence of COPD in a nationally representative US sample. Methods: NHANES 2007-2010 spirometry data were analyzed. Among those aged 40-79 years, 5,823 received the pre-bronchodilator spirometry. Those with likely airflow limitation were selected for the post-bronchodilator test (n=1,110). Airflow limitation was defined based on two criteria: 1) forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) < 70%1,2; and 2) FEV1/FVC < lower limit of normal (LLN) according to age, sex, height, and race/ethnicity1,3,4. Persons were classified as having chronic obstructive pulmonary disease (COPD) based on 1) having airflow limitation as defined above using pre- or post-bronchodilator values, or 2) reporting the use of daytime supplemental oxygen therapy plus a physician diagnosis of COPD (ever had emphysema or current chronic bronchitis). The final analytic samples for the pre-bronchodilator and post-bronchodilator analyses were 77.1% (n=5,477) and 50.8% (n=564) of those eligible, respectively. To account for this non-response in the estimation of COPD, we used a method where NHANES examination weights were adjusted to the eligible pre-bronchodilator and post-bronchodilator subpopulations. Results: In 2007-2010, using the FEV1/FVC ratio <0.7 diagnostic criterion and pre-bronchodilator test results, the estimated prevalence of COPD was 20.9% (SE 1.1) among US adults aged 40-79 years. Applying the same criterion to post-bronchodilator test results, the prevalence was 14.0% (SE 1.0). Using the FEV1/FVC ratio <LLN diagnostic criterion and pre-bronchodilator test results, the estimated prevalence of COPD was 15.4% (SE 0.8), while applying the same diagnostic criterion to post-bronchodilator test results, the prevalence was 10.2% (SE 0.8). Conclusions: The overall prevalence of COPD among US adults aged 40-79 years varied from 10.2% to 20.9% based on whether pre- or post-bronchodilator values were used and which diagnostic criterion (fixed ratio or LLN) was applied. The overall prevalence decreased by approximately 33% when airflow limitation was based on post-bronchodilator as compared to pre-bronchodilator spirometry, regardless of which diagnostic criterion was used.
Respiratory-system-disorders; Pulmonary-system-disorders; Lung-disorders; Humans; Health-surveys; Spirometry; Pulmonary-function-tests; Lung-function; Airway-obstruction; Information-retrieval-systems; Age-factors; Sex-factors; Height-factors; Racial-factors; Oxygen-therapy; Clinical-diagnosis; Statistical-analysis; Men; Women
T. Tilert, CDC/National Center for Health Statistics, Hyattsville, MD