Why Reference Equations for Lung Function Are Dropping Race

Major societies are replacing race-specific spirometry equations with a single race-neutral standard called GLI Global, because race is a social category rather than a biological fact about the lungs. Nothing about the airways changes; the reference does. For many Black patients the predicted normal rises, so the same breath now reads as more impairment, a shift that on current evidence lines up better with real mortality and flare risk. It is a change of yardstick, not of lungs.

What the old equations were doing

Spirometry compares your measured breath (chiefly FEV1, FVC, and their ratio) against a predicted value for someone of your age, sex, and height. The Global Lung Function Initiative's 2012 equations added race into that prediction and set a lower predicted normal for Black and Asian patients. Practically, a Black patient's result was graded against a lower bar, so a given FEV1 counted as a higher percent of predicted and was less likely to cross the threshold for abnormal. The stated intent was to reflect observed population averages. The effect was to build average differences into the definition of healthy, which quietly raised the amount of measured impairment a Black patient could carry before a test called it disease.

Why race went in, and why that logic gave way

The habit is old. Nineteenth-century spirometry already applied a downward correction for Black lungs, and later reference sets carried the assumption of innate, fixed differences forward. The 2023 American Thoracic Society statement lays out the problem plainly: race is a social category, not a genetic one, and the gaps once attributed to biology track far better with exposures such as air pollution, housing quality, nutrition, occupational hazard, and poverty. Coding those exposures as immutable race can mask real, modifiable harm, and it can normalize lower lung function in exactly the groups already carrying more environmental burden. A majority of the society's workshop panel endorsed moving toward race-neutral reference equations for interpretation.

From percent predicted to z-scores

The Breathe review from the European Respiratory Society explains the second, quieter half of the change: how abnormal gets defined. Percent predicted (say, below 80 percent) is easy to state but statistically crude, because the normal spread is not the same at every age and height. The z-score expresses how far a result sits from the predicted mean in standard deviations, and the lower limit of normal is set at the 5th percentile, a z-score of about 1.64 below the mean. Severity is then graded on the z-score scale rather than on percent-predicted cut points. Pairing the GLI Global equation with z-scores is the technical core of what race-neutral interpretation now means.

What actually changes on the report

This is where it becomes concrete. In the JAMA Network Open analysis of more than 8,000 adults, switching from the race-specific 2012 equations to race-neutral ones moved impairment labels in opposite directions by race. Restrictive-pattern findings among Black adults rose from about 27 percent to 38 percent, while among White adults they fell from roughly 23 percent to 18 percent. Graded severity increased in close to a quarter of Black participants and decreased in a similar share of White participants. Same people, same spirometers, different labels.

The larger COPDGene study, published in the American Journal of Respiratory and Critical Care Medicine in 2024 and covering more than 10,000 participants, reported that self-identified race was a major determinant of how obstruction severity redistributed when the reference changed. When severity was graded on the z-score scale rather than on percent-predicted cut points, the share of Black and White participants who shifted categories was more comparable, and the new grades matched clinical risk more closely.

The trade-offs worth naming

The case for the change is not abstract fairness alone; it also tracked outcomes better. In COPDGene, the race-neutral z-score classification separated survival and exacerbation risk across severity classes more consistently than the older grading, which had failed to distinguish mortality between normal spirometry and the mildest obstruction grade. Better calibration to hard outcomes is a strong argument.

But the reclassification cuts both ways, and honesty requires saying so. For a Black patient, being recognized as more impaired can mean earlier diagnosis, stronger support for a work-related injury claim, and access to treatment sooner. It can also mean a result that now falls below a threshold used in job screening, or fresh anxiety about a lung that works exactly as it did last year. Eligibility for some clinical trials and for certain disability or occupational determinations can move in either direction depending on where the cut points land. These are real consequences of moving the reference, and they fall on real people.

The honest bottom line

A reference equation is a population average, and no equation, race-neutral or otherwise, measures the person in front of you. The shift removes a variable that never carried genuine biological meaning and, on the best current evidence, lines up better with survival and flare risk. It does not settle every downstream question about thresholds, and it should not be read as a verdict on any single patient. This is educational information, not medical advice; anyone whose spirometry looks different after a lab updated its equations should ask the ordering clinician what changed and why.