Effects of adopting the new global lung function initiative 2012 reference equations on the interpretation of spirometry

Background: The recently generated spirometry reference equations from the Global Lung Function Initiative (GLI2012) provide a long-awaited opportunity for the adoption of a globally applicable set of normal reference values.

Objective: The aim of this study was to document the likely interpretative effects of changing from commonly used current spirometry reference equations to the GLI2012 equations on interpretation of test results in a clinical spirometry dataset.

Methods: Spirometry results from 2,400 patients equally distributed over the age range of 5-85 years were obtained from clinical pulmonary function laboratories at three public hospitals. The frequency of obstruction [FEV1/FVC below the lower limits of normal (LLN)] and spirometric restriction (FVC below the LLN) was assessed using the GLI2012, the National Health and Nutrition Assessment Survey (NHANES III), the European Community of Steel and Coal (ECSC) and the Stanojevic all-ages reference equations.

Results: The rates of obstruction (range 20.0-28.5%) and spirometric restriction (range 14.2-25.8%) were similar across the four sets of reference equations. The highest level of agreement with the new GLI2012 equations was seen with the NHANES III equations (97.6% for obstruction and 93.6% for spirometric restriction) and the lowest with those from the ECSC (96.0 for obstruction and 92.0% for restriction). These data can be used to estimate likely diagnostic spirometry interpretation effects in the clinical setting when switching to GLI2012 spirometry reference data.

Conclusions: We have found the effects on interpretation of changing to GLI2012 reference data to be minimal when changing from NHANES III and most significant when changing from ECSC reference data.