Implications of adopting the Global Lungs Initiative 2012 all-age reference equations for spirometry

The aim of this study was to determine the diagnostic and interpretative consequences of adopting the Global Lungs Initiative (GLI) 2012 spirometric prediction equations. We assessed spirometric records from 17 572 subjects (49.5% females), aged 18-85 years, from hospitals in Australia and Poland. We calculated predicted forced expiratory volume in 1 s (FEV1), forced expiratory volume (FVC), FEV1/FVC and lower limits of normal (LLN) using European Community for Steel and Coal (ECSC), National Health and Nutrition Examination Survey (NHANES) III and GLI 2012 equations. Obstruction was defined as FEV1/FVC<LLN and a restrictive pattern as FEV1/FVC>LLN and FVC<LLN. Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 2 and higher was defined as FEV1/FVC <0.70 and FEV1 <80% pred. GLI 2012 equations produce similar predicted values for FEV1 and FVC compared with NHANES, but produce larger values than ECSC. Differences in the LLN lead to an important increase in the prevalence rate of a low FVC compared to ECSC, and a significant decrease compared to NHANES prediction equations. Adopting GLI 2012 equations has small effects on the prevalence rate of airway obstruction. GOLD stages 2-4 lead to >20% underdiagnosis of airway obstruction up to the age of 55 years and to 16-23% overdiagnosis in older subjects. GLI 2012 equations increase the prevalence of a "restrictive spirometric pattern" compared to ECSC but decrease it compared to NHANES.