Introduction

Spirometry tests play a pivotal role in diagnosing airway obstruction, severity of respiratory impairment, in monitoring health, evaluating response to treatment and in pre-operative assessment of subjects. However appropriate interpretation of results is reliant on knowledge of the normal range of values observed in healthy people. For most biochemical indices the normal range is independent of sex, age and ethnic group. The values observed are typically within narrow limits because of the bodies feedback control system. Conversely, the interpretation of spirometric test results is complicated by the fact that "normal values" vary with age, height, sex and ethnic group, and the limits of normal are also age dependent. 

Until recently it was not possible to satisfactorily describe the age-related growth and decline of lung function with age. As a result a discontinuous approach was adopted, which entailed deriving multiple prediction equations for different age groups. Inevitably they connected poorly at the transition from one to the next. Many of the older reference developed used simple statistical analyses, which did not adequately describe the dependency of lung function values on height, age, sex and ethnicity. The pioneering work of Stanojevic et al. (1) changed all this and gave rise to the Global Lung Function Initiative, a Task Force of the European Respiratory Society and American Thoracic Society  Global Lung Function Initiative. The Task Force produced GLI reference equation (2) that are endorsed by the European Respiratory Society, American Thoracic Society, Australian and New Zealand Society of Respiratory Science, Asian Pacific Society for Respirology, the Thoracic Society of Australia and New Zealand, and the American College of Chest Physicians, and many other professional bodies.

This section describes the history and evolution of reference equations for spirometry, details about how GLI reference equations were developed and interpretative strategies for research and clinical use.

Philip H. Quanjer - Sanja Stanojevic - Janet Stocks - Tim J. Cole

References

1. Stanojevic S, Wade A, Stocks J, et al. Reference ranges for spirometry across all ages. A new approach. Am J Respir Crit Care Med 2008; 177: 253–260. Manuscript
2. Quanjer PH, Stanojevic S, Cole TJ, et al. and the ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95 years age range: the Global Lung Function 2012 equations. Eur Respir J 2012; 40: 1324-1343. PubMed

For more information, go to: lungfunction.org