Choosing the most appropriate reference values for an individual can be difficult. The assignment of ethnicity for an individual can be uncertain, particularly for those of mixed ethnicity. Good data is lacking for many populations and there may be morphologic changes with subsequent generations of an immigrant population. Shown below are the populations for which each of the GLI-2012 equations are known to be representative.
In addition to the countries listed, it would be reasonable to apply the group reference equations to others with geographic or ethnic proximity. Thus the Caucasian equations could be used for any person having origins in any of the original peoples of Europe, the Middle East, or North Africa and for any non-indigenous person of South America. Similarly, the Southeast Asian equations may be reasonably extended throughout that region.
However, significant populations remain missing, including Native Americans, Alaska Natives, the Indian sub-continent and Japan. There are many reports of spirometry reference values (and some for other tests) from individual countries or ethnic groups, but the population size and data quality may vary.
For individuals of Japanese origin the following source could be used:
Kubota M, etal Reference values for spirometry, including vital capacity, in Japanese adults calculated with the LMS method and compared with previous values. Respir Investig 2014; 52(4): 242-250).
Within the Indian sub-continent, there appear to be regional differences in spirometry values that cannot be encompassed in the same equations.
GLI-2012 provides a fifth set of equations, “Other”, made up as a combination of the four groups above, which may be applied as a first approximation to individuals not represented by one of the groups or who are of mixed ethnicity. This should be noted in the report and results interpreted with awareness of increased uncertainty.
This figure summarizes crudely which GLI equations could be used for individuals with family origins in different regions of the world.