Reliability of portable spirometry performed in the Korea national health and nutrition examination survey compared to conventional spirometry

Background: The Korea National Health and Nutrition Examination Survey (KNHANES) is a well-designed survey to collect national data, which many researchers have used for their studies. In KNHANES, although portable spirometry was used, its reliability has not been verified. Methods: We prospectively enrolled 58 participants from four Korean institutions. The participants were classified into normal pattern, obstructive pattern, and restrictive pattern groups according to their previous spirometry results. Lung function was estimated by conventional spirometry and portable spirometry, and the results were compared. Results: The intraclass correlation coefficients of forced vital capacity (FVC) (coefficient, 9.993; 95% confidence interval [CI], 0.988-0.996), forced expiratory volume in 1 second (FEV₁) (coefficient, 0.997; 95% CI, 0.995-0.998), FEV₁/FVC ratio (coefficient, 0.995; 95% CI, 0.992-0.997), and forced expiratory flow at 25-75% (FEF25-75%; coefficient, 0.991; 95% CI, 0.984-0.994) were excellent (all p<0.001). In the subgroup analysis, the results of the three parameters were similar in all groups. In the overall and subgroup analyses, Pearson's correlation of all the parameters was also excellent in the total (coefficient, 0.986-0.994; p<0.001) and subgroup analyses (coefficient, 0.915-0.995; p<0.001). In the paired t-test, FVC, FEV₁/FVC, and FEF25-75% estimated by the two instruments were statistically different. However, FEV₁ was not significantly different. Conclusion: Lung function estimated by portable spirometry was well-correlated with that estimated by conventional spirometry. Although the values had minimal differences between them, we suggest that the spirometry results from the KNHANES are reliable.