Introduction: The selection of reference equations for spirometry interpretation can significantly influence the diagnosis of disease. Global Lung Function Initiative (GLI) Global equations have recently been derived as an alternative to race specific equations. This study investigated the clinical impact of GLI Global equations (Bowerman et al, AJRCCM, 2022) compared to GLI Caucasian equations, used as standard at our centre, on the interpretation of spirometry in children.
 
Methods: Retrospective analysis of paediatric spirometry tests performed for a clinical indication at the Hospital for Sick Children, Toronto, from January to December 2022.
 
Results: 2421 spirometry tests were included, 943 (39.0%) from non-Caucasian patients. The use of GLI Global resulted in more tests categorized as normal (57.5% vs. 63.5%, p<0.05) and fewer suggestive of restriction (17.9% vs. 10.8%, p<0.05), compared to GLI Caucasian. There were a similar proportion with a low FEV1/FVC and low FEV1 (9.5% vs 9.5%, p=0.92) but a higher proportion with low FEV1/FVC and normal FEV1 (7.3% vs. 11.2%, p<0.05). 163 (6.7%) tests initially interpreted as restriction were reclassified as normal. Of these, 50.9% had underlying medical conditions such as cardiac defects (n=31), oncologic disease (n=23), bone marrow transplant (n=16), and sickle cell disease (n=13), that increase the risk of restrictive lung disease.

Conclusions: In a diverse paediatric population, GLI Global equations reduced the number of spirometry tests suggestive of restriction, which may underdiagnose lung disease in some children. The use of GLI Global may require a greater level of caution when assessing values close to the lower limits of normal.