Background: Chronic obstructive pulmonary disease (COPD) has a variable natural history and not all individuals follow the same course. This study aimed to identify the prevalence and characteristics of asymptomatic COPD patients from a population-based survey in China.
Methods: A multistage cluster sampling strategy was used in a population from seven different provinces/cities. All residents (over 40 years old) were interviewed with a standardized questionnaire and spirometry. Post-bronchodilator forced expiratory volume in 1 second (FEV(1))/forced vital capacity (FVC) of less than 70% was defined as the diagnostic criterion of COPD. All COPD patients screened were divided into symptomatic group and asymptomatic group according to the presence or absence of chronic respiratory symptoms. Socio-demographic, personal and exposure variables were collected and analyzed.
Results: Among the 1668 patients who were diagnosed with COPD from the 25 627 sampling subjects, 589 (35.3%) were asymptomatic. The age, sex, body mass index (BMI), rural and urban distributions, smoking habit and education levels were similar in the two groups. A total of 64.7% of the asymptomatic patients had no comorbidities. Cardiovascular diseases and lung cancer were more common among symptomatic COPD patients than asymptomatic group. Asymptomatic COPD group were less likely to present with poor ventilation in the kitchen, a family history of respiratory disease and recurrent childhood cough. Asymptomatic COPD patients had significantly higher FEV(1) (73.1% vs. 61.0%), FVC (91.9% vs. 82.0%), and a higher ratio of FEV(1)/FVC (62.9% vs. 58.7%) (all P < 0.001) than symptomatic group. More asymptomatic patients were underdiagnosed (91.9% vs. 54.3%, P < 0.001) than symptomatic patients.
Conclusions: This large population-based survey confirmed a high prevalence of asymptomatic COPD patients in China. More use of spirometry screening test may be important to the early detection of COPD.