Appropriate interpretation of longitudinal spirometry assessments

Introduction: Recommendations for spirometry interpretation have used reference equations based on white subjects switching from paediatric to adult ranges after 18 years of age, with limitations previously described. Aims: In 2012, the Global Lung function Initiative (GLI) released reference equations providing a continuous equation from 3 to 95 years and adjusting for ethnic differences. This case study compared spirometry based on Rosenthal/ECCS with GLI predicted equations. Methods: Seventeen spirometry assessments performed in a Black subject (age 12-18y) with Juvenile dermatomyositis (JDM) were expressed as % predicted using the Rosenthal ( 18y), without ethnic adjustment, compared with the Black-specific GLI equations. Results: FEV1 % predicted was up to 9% higher using GLI compared with old standards. ![Figure][1] After 18y there was an increase in FEV1 by 100mL, reflected by the increase in GLI % predicted, whereas ECCS reference data showed a reduction in FEV1 % predicted by 2%, due to switching from paediatric to adult equations. If a fixed "normal" threshold of 80% predicted had been applied, the subject would have been misdiagnosed on 6 occasions. Conclusion: Failure to adjust for ethnicity and using discontinuous equations can lead to spirometry misinterpretation and misdiagnosis when the 80% predicted cut-off for abnormality is used. The advantages of using GLI 2012 reference equations has been demonstrated. [1]: pending:yes