In May 2012 the Global Lung Function Initiative (GLI) Task Force published Multi-ethnic reference values for spirometry for the 3-95 year age range: the global lung function 2012 equation. This was the first study to present spirometry prediction equations spanning 3‐95 years for ethnic and geographic groups from 26 countries. In September 2013 the ARTP officially endorsed the GLI spirometry reference equations. Implementation of GLI was one of the annual objectives this year.
Members of the GLI implementation group:
Dr Jane Kirkby (GLI Implementation Strategy Group Lead)
Prof Janet Stocks (GLI-ISG Professional Advisor)
Dr Karl Sylvester (GLI-ISG Group Member)
Dr Brendan Cooper (GLI-ISG Group Member)
What was the Global Lung Function Initiative (GLI)?
The GLI network comprised of 234 registered individuals (clinicians, researchers, technicians, IT engineers, and manufacturers) from 41 countries across 5 continents. During the data collection period they collated over 150,000 spirometry data points. After extensive data cleaning and exclusions (e.g. due to missing ethnic groups or suboptimal quality control) and use of advanced statistical techniques (the LMS method (lambda-mu-sigma) that allows the development of smoothed curves and efficient calculation of z scores simultaneously) the first all-age, global multi-ethnic reference equations for spirometry based on ~74,000 healthy non-smoking subjects aged 3-95years was published in the European Respiratory Journal.1
Why should we use GLI reference equations?
The principles behind normative reference data are based upon the theory that a summary measure of values obtained from “normal” individuals will represent the range of values expected in a healthy population. A literature search on pubmed will reveal over 300 spirometry reference equations relating to all sorts of differing populations, age-groups and nationalities,2 hence it can be challenging to decide which one to apply. Although there are published, evidence-based recommendations on equipment specifications, spirometry performance and identification on technical acceptability,3-5 it is largely the users responsibility to select the most appropriate reference equation for their population. Until last year (2013) the ARTP recommended the European Coal and Steel Community (ECSC) equations for adults6 and Rosenthal for children.7
Why have the recommendations changed?
The ECSC was the first organisation to issue recommendations for spirometry in 1960, and issued predicted values in 1971. Rapid technological developments lead to a revision of the ECSC report in 1983 (this included lung volumes), and further updates in 1987 (to include TLCO), 1993 and 1994. Hence the recommendations were combined sets of reference values across several decades. Furthermore, the sets of reference values issued by the ECSC were based on Caucasian males aged 18-75yr working in coal mines and steel works, and although no women were tested, the ECSC issued reference values for females (80% of the values for males). Thus the ECSC is not representative of the population we measure today. In paediatrics, the “Brompred” Rosenthal reference equations were based on 772 (455 male) Caucasian children aged 4-19years. It included pubertal assessments (Tanner assessments developed in 1962) to adjust for varying thoracic dimensions during puberty, however pubertal assessments are rarely measured in the clinical paediatric lung function laboratory, resulting in arbitrary break points for puberty and further changes during transition to adult care. Finally the use of traditional linear regression equations to develop the ECSC and Rosenthal reference equations was limited since the relationship between lung function, age and body size is not linear. Use of advanced statistical techniques such as the LMS method is essential when adjusting for the complexities of the determinants of lung function (age, height sex and ethnicity).
The publication of the new GLI All-age, multi-ethnic reference equations have overcome many of the limitations previously experienced. Philip Quanjer, the lead author for the ECSC has worked tirelessly in his retirement to update his reference equations. On a recent discussion with him he stated: “We have known for years that these (ECSC equations) are wanting, and they are now superseded by the GLI-2012 equations which have been shown in a number of studies to fit various populations, cover a very large age range, can be applied to a number of ethnic groups.” The ARTP now recommend the use of GLI spirometry reference equations.
Previously recommended equations have been shown to be outdated. Both the lead author of the ECSC equations and all international professional respiratory bodies have now recommended the use of GLI reference equations. We are doing our patients a dis-service if we knowingly apply inappropriate reference equations, and must now make a concerted effort to ensure we apply the most appropriate techniques for interpreting spirometry.