Background: Previous analysis of survey data from a study in older urban Thai persons reported prevalence of chronic obstructive pulmonary disease (COPD) of 7.11% according to formerly recommended criteria that used fixed ratio (70%) of pre-bronchodilator FEV1/FVC as the cut-off value. In 2012, the Global Lung Initiative (GLI)-2012 equations for spirometric reference were established and the diagnostic criteria for COPD were changed.

Objective: To reanalyze the data collected during the 2002 respiratory health survey to determine prevalence of COPD in older urban Thai persons according to the new GLI-2012 equations.

Material and Method: Demographic and clinical data of 3,094 subjects aged ≥60 years from 124 urban communities were re-analyzed. Prevalence of COPD determined by post-bronchodilator FEV1/FVC and GLI-2012 equations using lower limit of normal by the Lambda-Mu-Sigma method (LMS-LLN) was compared to COPD prevalence findings based on criteria used in previous analysis.

Results: Prevalence of COPD in the study population using post-bronchodilator FEV1/FVC and LMS-LLN was 6.50% (95% CI: 5.63-7.37), compared with 7.82% (95% CI: 6.87-8.77) when fixed ratio (70%) of FEV1/FVC was used as cut-off. Diagnostic agreement of COPD between LMS-LLN and fixed ratio was high (kappa 0.88, p<0.0001). However, 45/242 (18.6%) subjects diagnosed as COPD by fixed ratio criteria were considered as “over-diagnosed” when LMS-LLN was used as the standard cut-off. The same comparison applied to subjects aged ≥80 years revealed an increased rate of over-diagnosis to 7/22 (31.8%) subjects. Higher agreement was observed (kappa 0.95, p<0.0001) when comparing between cut-offs for diagnosis of “at least GOLD stage II” COPD.

Conclusion: Prevalence of COPD in older urban Thai persons was lower when LMS-LLN was substituted for fixed ratio (70%) of FEV1/FVC. Agreement in COPD diagnosis between both criteria was high, but a substantial proportion of subjects may be over-diagnosed.

Keywords: Aged, COPD, Epidemiology, Prevalence, Spirometry