Differences in severity grading of lung hyperinflation using GLI versus ECSC reference values

In 2021, the Global Lung Initiative (GLI) network recommended new static volume lung function reference equations, setting new normal ranges for lung hyperinflation indices and, as a result, for the classification of lung hyperinflation severity. This study examined how use of the GLI 2021 reference equations affected the detection of lung hyperinflation and the distribution of lung hyperinflation severity based on the lung hyperinflation severity grading scale, which relies on fixed % predicted cut-offs and z-scores.

An analysis was performed on data from 12 535 body plethysmography recordings performed from January 2013 to June 2023. The GLI 2021 and the European Coal and Steel Community (ECSC) reference equations were used to calculate the z-scores for residual volume (RV), total lung capacity (TLC) and RV/TLC. The % predicted RV/TLC ratios were calculated and the distribution of lung hyperinflation severity grading was assessed.

Using % predicted cut-offs, severe lung hyperinflation was observed more frequently using the GLI 2021 reference equation compared with the ECSC reference equation (27% versus 8.8%, p<0.001), while mild lung hyperinflation was identified in 7% of the recordings using the GLI 2021 references (versus 21% using ECSC; p<0.001). Grading using the GLI 2021 reference equations and z-scores produced a similar distribution of lung hyperinflation severity to the use of % predicted cut-offs and ECSC reference equations.

The study highlights a significant difference in lung hyperinflation grading using GLI 2021 reference equations, necessitating review of the severity scale when using % predicted cut-offs and z-scores with GLI 2021 reference equations.