Evaluation of the global lung function initiative 2012 reference values for spirometry in a Swedish population sample

Background: The Global Lung Function Initiative 2012 (GLI) reference values are currently endorsed by several respiratory societies but evaluations of applicability for adults resident in European countries are lacking. The aim of this study was to evaluate if the GLI reference values are appropriate for an adult Caucasian Swedish population. Methods: During 2008-2013, clinical examinations including spirometry were performed on general population samples in northern Sweden, in which 501 healthy Caucasian non-smokers were identified. Predicted GLI reference values and Z-scores were calculated for each healthy non-smoking subject and the distributions and mean values for FEV1, FVC and the FEV1/FVC ratio were examined. The prevalence of airway obstruction among these healthy non-smokers was calculated based on the Lower Limit of normal (LLN) criterion (lower fifth percentile) for the FEV1/FVC ratio. Thus, by definition, a prevalence of 5% was expected. Results: The Z-scores for FEV1, FVC and FEV1/FVC were reasonably, although not perfectly, normally distributed, but not centred on zero. Both predicted FEV1 and, in particular, FVC were lower compared to the observed values in the sample. The deviations were greater among women compared to men. The prevalence of airway obstruction based on the LLN criterion for the FEV1/FVC ratio was 9.4% among women and 2.7% among men. Conclusions: The use of the GLI reference values may produce biased prevalence estimates of airway obstruction in Sweden, especially among women. These results demonstrate the importance of validating the GLI reference values in different countries.