Characteristics and risk factors of patients with undiagnosed COPD in China: results of a nationwide study from the 'Happy Breathing' Programme with mixed methods evaluation.

Objectives: Due to the big disease burden of undiagnosed chronic obstructive pulmonary disease (COPD), we aimed to investigate the differences in the characteristics and risk factors of patients with undiagnosed COPD in China.

Methods: We used data from the 'Happy Breathing' Programme through April 2023. Current study is a cohort design. Participants were divided into high risk, undiagnosed and diagnosed COPD. Univariate logistic regression, lasso regression, decision tree, random forest and gradient boosting machine were used to screen the variables. Comparisons were conducted between undiagnosed and patients with diagnosed COPD.

Results: A total of 1603 high-risk, 4688 undiagnosed and 1634 patients with diagnosed COPD were identified. Patients with undiagnosed COPD had the lowest level of education, the poorest COPD-related knowledge and most biofuel users compared with high-risk populations and diagnosed patients (p<0.001). After multivariable logistic regression analysis, COPD-related knowledge score (OR=0.96, 95% CI 0.95 to 0.97), COPD Assessment Test Score (OR=1.01, 95% CI 1.00 to 1.02) and modified Medical Research Council Dyspnea Scale (OR=1.26, 95% CI 1.14 to 1.39) remained significant. Analysis of follow-up data showed that patients with undiagnosed COPD had lighter symptoms and experienced less acute exacerbations than diagnosed patients (p<0.001).

Discussion: Most patients with COPD remain undiagnosed until they feel dyspnoea or hospitalisation due to acute exacerbation. Undiagnosed COPD contributes significantly to the disease burden.

Conclusion: In China, patients with undiagnosed COPD were poorly educated, consumed more biofuels, smoked more and had limited COPD-related knowledge. Patients with undiagnosed COPD are also at risk of acute exacerbation.

Trial registration number: NCT04318912.