By Ray Wright, Advanced Medical Engineering · 2026-08-17

GLI-2012, GLI Global 2022 and 'GLI Other': which predicted values to use for South African patients

Predicted values decide whether a result is called normal or abnormal. In South Africa the choice of equation carries a history, and the wrong choice can hide disease in some patients and invent it in others. Here is what the options are and how to choose.

What a reference equation does

A spirometry report compares the patient's FEV1, FVC and ratio with what is expected for someone of the same age, height and sex. That expectation comes from a reference equation fitted to a healthy population. Two things follow. First, the answer depends on which population the equation was built from. Second, the honest way to report the comparison is as a z-score (how many standard deviations from expected) with a lower limit of normal, not as a single percent-predicted with a fixed 80% cut-off, because normal variation is wider at some ages and heights than at others.

GLI-2012

The Global Lung Function Initiative 2012 equations were fitted to data from tens of thousands of healthy people across many countries and cover ages 3 to 95, so a child and an adult are on one continuous curve. GLI-2012 provides separate equations for several population groups (labelled Caucasian, African-American, North-East Asian, South-East Asian) and an "Other" group for people not represented by those, computed as an average. South African guidance has referenced GLI-2012 since it appeared, and it remains widely used in local practice.

Why race-neutral GLI Global 2022 exists

The population-specific equations in GLI-2012 embed the assumption that healthy lung function differs by ancestry. Evidence has accumulated that much of the measured difference tracks socioeconomic and environmental exposure rather than biology, and that using a lower "expected" value for some groups sets a lower bar for calling their results abnormal, which delays diagnosis and can affect compensation and fitness decisions. In 2022 the GLI published a single race-neutral equation set derived from the same data with the population term removed. Its use is now recommended by major respiratory societies. In a South African setting, where the older population labels map poorly onto real ancestry and where occupational compensation depends on the result, the case for a race-neutral equation is strong.

What "GLI Other" means

"GLI Other" is the GLI-2012 option for people not represented by the named groups: it is the average of the group equations. It has been used in South Africa as a pragmatic choice for patients of African and mixed ancestry. It is not a South African equation and it is not race-neutral in the 2022 sense; it is a middle value. Software that offers it should say so on the report.

Choosing, and staying consistent

• Default to race-neutral GLI Global 2022 for new programmes and new patients, and report z-scores and LLN.
• Do not switch equations silently between years. A change of equation moves percent-predicted without the lungs changing. If a programme moves from GLI-2012 to GLI Global 2022, re-express the baseline under the new equation, or compare z-scores computed under one equation, and note the change in the file.
• Never let the software guess. If ethnicity is missing, the software must not silently pick a group. It should either use the race-neutral equation or ask.
• Name the equation on every report. A number without its equation cannot be checked or reproduced.
• Interpret with z-scores. A z-score below -1.645 is below the LLN. Percent-predicted stays useful for talking to patients but should not decide the diagnosis on its own.

Paediatrics and older adults

GLI equations run continuously from age 3 to 95, which removes the old jump between paediatric and adult equations at 18. That matters for adolescent apprentices and for older workers approaching retirement, where the older equations extrapolated badly. For very short or very tall patients, and at the extremes of age, the z-score is more reliable than the percent.

What SpiroWright does

SpiroWright ships GLI-2012 (LMS) and race-neutral GLI Global 2022, with GLI Other, NHANES III and ECCS available where a programme requires them; it reports z-scores, LLN/ULN and percent-predicted, prints the equation source on the report, and does not fall back to a default ethnicity when the field is blank. See ATS/ERS 2019 in SpiroWright.

Further reading: Quanjer PH et al. Multi-ethnic reference values for spirometry for the 3 to 95 year age range: the Global Lung Function 2012 equations. Eur Respir J 2012;40:1324-1343. Bowerman C et al. A race-neutral approach to the interpretation of lung function measurements. Am J Respir Crit Care Med 2023;207:768-774.

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