Adult reference values for spirometry, body plethysmography and diffusing capacity adjusted for sex, age, weight, height or arm span - the Danish lung function material (DALFUMAT) study

Objectives: The study aimed to develop new national reference values for dynamic and static lung volumes, as well as diffusing capacity for carbon monoxide, measured in the same participants. These values were compared with existing reference values from GLI and ECCS. Additional aims included the development of lung function reference values based on arm span, the establishment of post-bronchodilator reference values for spirometry, the creation of reference values for bronchodilator response, and the identification of significant bronchodilator responses using z-scores. Furthermore, the study sought to observe and enhance the quality of Danish lung function laboratories. Methods: Spirometry, body plethysmography, single-breath diffusion capacity, and bronchodilator testing were performed on 908 healthy non-smokers aged 18-97 years, selected from municipalities served by 13 participating Danish centres. Strict quality control was maintained in accordance with ATS/ERS standards. Sex, age, age squared, weight, and height (or arm span) were used as independent variables in the multiple regression equations. The resulting lung function data were compared with predicted values from GLI and ECCS. Results: Sex-specific reference equations were established for 29 lung function parameters. Additionally, reference values based on arm span and post-bronchodilator spirometry were calculated, and bronchodilator response was established using four different endpoints, including z-scores. A substantial proportion of the new reference values differed clinically significantly from those predicted by GLI and ECCS equations. These discrepancies were more frequent in females than males, more pronounced for ECCS than GLI, and more common for flow and volume parameters than for diffusion capacity and ratios. Conclusion: Given that many of the new reference values differ clinically significantly from those provided from GLI and ECCS, we recommend the nationwide adoption of the new DALFUMAT reference values.