Variability of the prevalence of undiagnosed airflow obstruct on in smokers using different diagnostic criteria

Purpose: To estimate the prevalence of undiagnosed airflow obstruction (AFO) in Hong Kong smokers with no previous diagnosis of respiratory disease, and to assess its variability when applying different prediction equations and diagnostic criteria. Methods: A multicenter, population-based, cross-sectional prevalence study was performed in smokers aged 20 to 80 years. Three different criteria (fixed 70% [Global Initiative for Chronic Obstructive Lung Disease and British Thoracic Society], fixed 75%, and European Respiratory Society [ERS]) were applied to define a lower limit of normal (LLN) of the FEV1/FVC ratio to compare with the Hong Kong Chinese reference equation (criterion 1), which had used a distribution-free method to obtain the lower fifth percentile of FEV1/FVC ratio as the LLN. Results: In 525 male patients, using criterion 1 (local internal prediction equation) and defining AFO as FEV1/FVC less than LLN, the overall prevalence of AFO was 13.7%: 8.3% in age >= 20 to 40 years, 14.0% in age >= 40 to 60 years, and 17.8% in age >= 60 to 80 years. When the local internal prediction equation was used as the comparison reference, the fixed-ratio methods tended to miss AFO in younger age groups and overdiagnose AFO in old age, while the ERS criteria, which uses an almost lower fifth percentile-equivalent method, showed less of such a trend but still only showed moderate agreement with criterion 1. Conclusions: Undiagnosed AFO was prevalent in Hong Kong smokers. Estimated prevalence rates were highly affected by the criteria used to define AFO. The predicted lower fifth percentile values calculated from a local reference equation as the LLN of FEV1/FVC ratio should be used for the diagnosis of AFO.