ABSTRACT: Background:Use of different spirometry reference equations can lead to misinterpretation of spirometry results. Currently, no study has been carried out to determine if there is any discordance between the interpretation of spirometry data using the Global Lungs Initiative (GLI) 2012, the Third National Health and Nutrition Examination Survey (NHANES III), the Knudson, and the Siriraj reference equations in Thai people. Therefore, this study aimed to determine differences and agreements regarding spirometry results using the GLI2012, NHANES III, Knudson, and Siriraj reference equations in a Thai population. Methods:A retrospective study was carried out using 2,492 spirometry results from Thai people (age ranged 8-80 years old) who were referred by their physicians for spirometry testing at the Lung Health Center, Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand between January 2005 and December 2015. The spirometry results were interpreted using four reference equations. Respiratory function patterns were classified as normal, spirometric restriction, obstruction, or mixed defect. The severity of abnormal patterns were classified as mild, moderate, moderately severe, severe or very severe. A Nominal Analysis of Variance (NANOVA) test was used to analyze differences in diagnosis and classification for the degree of severity. The Kappa statistic was used to determine agreements of spirometry results between four reference equations. Results:The differentiation in both spirometry diagnosis and the severity classification were significant across the four reference equations (P<0.001). However, the levels of agreement among the four reference equations were moderate to good (Kappa values ranged from 0.56 to 0.77 for the diagnosis and 0.67 to 0.82 for the severity). Conclusions:The results of this study suggest that the use of the GLI2012, NHANES III, Knudson, and Siriraj reference equations alters the interpretation of spirometry data in this population of Thai adults.
