Jul 15, 2026 Race-Neutral GLI Equations, Z-Scores, and DLCO
The transition to race-neutral pulmonary function test (PFT) interpretation represents one of the most significant changes in respiratory diagnostics in decades. As laboratories adopt the latest GLI Global reference equations, pulmonologists and pulmonary function laboratory directors are reevaluating how spirometry, lung volumes, and diffusing capacity (DLCO) should be interpreted under a unified, race-neutral framework.
The shift is about more than replacing prediction equations. It changes how clinicians evaluate normality, interpret z-scores, communicate results, and compare patients over time. It also requires laboratories to ensure their software, workflows, and reporting systems reflect current recommendations from leading respiratory societies.
For practices performing complete pulmonary function testing, these updates extend beyond spirometry. Understanding how race-neutral spirometry, race-neutral DLCO, and lung volume interpretation work together provides a more comprehensive picture of pulmonary physiology while supporting greater consistency across diverse patient populations.
In this article, we’ll explain what changed, how the GLI Global reference equations work, and what pulmonary practices should consider when updating their testing protocols.
What Changed in 2026 for PFT Interpretation
Pulmonary function interpretation has steadily evolved over the past several years as international respiratory organizations sought to improve consistency and reduce unintended bias in diagnostic testing.
Historically, many pulmonary function systems used race-specific reference equations that adjusted predicted values based on self-identified race or ethnicity. Although these equations were developed using available population data, concerns grew regarding whether race should be incorporated into physiologic reference standards, given that race is a social construct rather than a direct biological measurement.
In response, the Global Lung Function Initiative (GLI Global) developed race-neutral reference equations designed to provide a single standard applicable across diverse populations. These equations have been increasingly adopted following guidance from major respiratory organizations, including the American Thoracic Society (ATS), helping standardize interpretation while reducing variability introduced by race-specific adjustments.
For pulmonary practices, this means several practical changes:
- Reference equations may produce different predicted values than legacy software.
- Z-scores become even more important than percent predicted.
- Lower Limits of Normal (LLN) may shift for individual patients.
- Longitudinal comparisons require awareness of which reference equations were used.
- Reporting systems should clearly identify the selected reference standards.
Rather than changing how pulmonary physiology is measured, the transition changes how results are interpreted.
Race-Neutral Spirometry: GLI Global Explained
The GLI Global reference equations were developed using international datasets that include hundreds of thousands of pulmonary function tests across a wide range of ages and geographic regions.
Unlike older race-specific models, the race-neutral equations use patient characteristics such as:
- Age
- Height
- Sex
- Physiologic variation
without requiring racial classification during interpretation.
This offers several advantages.
Improved Standardization
Large healthcare systems often serve highly diverse patient populations.
Using one consistent reference standard simplifies interpretation across
clinics, hospitals, and pulmonary laboratories.
Reduced Administrative Complexity
Race-neutral equations eliminate the need to document race solely for
pulmonary function interpretation, reducing workflow complexity and
minimizing inconsistent classification.
Better Alignment with Current Guidelines
Many professional societies now recommend transitioning toward
race-neutral interpretation for spirometry. Using current reference
equations helps laboratories remain aligned with evolving standards
while supporting consistent reporting practices.
Importantly, clinicians should remember that measured values never change.
If a patient’s FEV₁ is 2.15 liters, it remains 2.15 liters regardless of
the reference equation. What changes is the predicted value, z-score, and
interpretation relative to the reference population.
Reading Z-Scores and the Lower Limit of Normal
As laboratories adopt the GLI Global reference equations, understanding z-score spirometry becomes increasingly important.
Historically, many clinicians focused primarily on percent predicted values. While percent predicted remains familiar, it has important limitations because normal variability differs by age, sex, and body size.
Why Z-Scores Matter
A z-score represents how far a patient’s measured value deviates from the
expected population average.
- 0 indicates an average expected value.
- -1 indicates one standard deviation below average.
- -1.645 approximates the Lower Limit of Normal (LLN).
- Values below the LLN are generally considered abnormal.
Using z-scores allows clinicians to compare patients of different ages
and body sizes more consistently than percent predicted alone.
Understanding the Lower Limit of Normal
The LLN replaces fixed cutoffs that may overdiagnose obstruction in
older adults or underdiagnose disease in younger patients.
For example, relying on a fixed FEV1/FVC ratio of 0.70 may
misclassify some patients. The GLI framework instead evaluates whether
the patient’s ratio falls below the statistically expected range for
someone of similar age and anthropometric characteristics.
This individualized approach improves diagnostic precision while
reducing age-related bias.
Reporting Considerations
Modern PFT software should clearly display:
- Measured values
- Predicted values
- Percent predicted
- Z-scores
- Lower Limit of Normal
- Interpretation category
Providing all of these values supports clinician confidence during
interpretation and longitudinal patient follow-up.
How Results Shift Across Patient Groups
One common question from clinicians is whether race-neutral equations will increase or decrease abnormal findings.
The answer is: it depends on the individual patient.
Because the race-neutral equations establish a different reference population, predicted values may increase for some individuals and decrease for others.
Potential effects include:
- Some previously normal spirometry results may now fall below the LLN.
- Other patients previously categorized as abnormal may now fall within normal limits.
- Disease severity categories may shift slightly in selected patients.
- Longitudinal trends should be interpreted carefully when changing reference equations.
These changes do not indicate worsening or improving lung function. Rather, they reflect a different statistical framework for comparison.
For clinicians managing chronic diseases such as COPD, asthma, interstitial lung disease (ILD), or pulmonary fibrosis, documenting when the laboratory transitions to updated reference equations can help avoid confusion during follow-up visits.
Practices should also educate referring physicians about the transition so interpretation changes are understood within the context of the new reference standards.
Race-Neutral DLCO and Lung Volume Reading
While discussions around race-neutral interpretation often focus on spirometry, complete pulmonary function testing extends well beyond airflow measurements.
For pulmonologists evaluating restrictive disease, emphysema, pulmonary vascular disorders, or interstitial lung disease, lung volumes and DLCO remain essential diagnostic tools.
This is where complete PFT systems provide a broader clinical perspective than spirometry alone.
Why DLCO Matters
Diffusing capacity evaluates how efficiently gases move across the
alveolar-capillary membrane.
DLCO plays an important role in evaluating:
- Interstitial lung disease
- Pulmonary hypertension
- Emphysema
- Connective tissue disorders
- Occupational lung disease
- Combined pulmonary fibrosis and emphysema
As race-neutral reference standards continue to expand across pulmonary
function testing, laboratories should ensure that DLCO interpretation
remains aligned with current recommendations while maintaining
consistency across all reported measurements.
Lung Volume Interpretation
Lung volume measurements, including Total Lung Capacity (TLC), Residual
Volume (RV), and Functional Residual Capacity (FRC), provide critical
information that spirometry alone cannot.
A patient with reduced FVC on spirometry may have:
- True restriction confirmed by reduced TLC
- Air trapping with preserved TLC
- Poor test effort
- Mixed obstructive and restrictive physiology
Without lung volume testing, these scenarios may appear similar despite
requiring different clinical management.
The Advantage of Complete PFT Reporting
When spirometry, lung volumes, and DLCO are interpreted together using
current reference standards, clinicians gain a more complete
understanding of pulmonary physiology.
This comprehensive approach supports more confident evaluation of
complex respiratory disease and helps ensure interpretation remains
consistent as laboratories transition to race-neutral reference
equations.
For pulmonary practices seeking to modernize testing workflows,
platforms capable of reporting spirometry, lung volumes, and DLCO
within a unified software environment simplify implementation of
updated standards while supporting comprehensive diagnostic evaluation.
Updating Reference Equations in Your Lab
Transitioning to the latest GLI Global reference equations involves more than a software update.
Laboratories should develop a structured implementation plan that includes clinical, technical, and educational considerations.
Key steps include:
Verify Software Compatibility
Ensure your pulmonary function software supports the latest GLI reference equations for spirometry, lung volumes, and DLCO where applicable.
Document the Transition
Record the implementation date so clinicians understand why interpretations may differ from previous reports.
Educate Staff
Pulmonary function technologists and interpreting physicians should understand:
- Changes in predicted values
- Z-score interpretation
- Updated LLN thresholds
- Reporting terminology
Communicate with Referring Providers
Primary care physicians, allergists, cardiologists, and other referring clinicians may notice interpretation differences. Proactive education helps prevent confusion.
Review Longitudinal Reports
Patients with serial pulmonary function testing should be interpreted carefully if older studies used different reference equations.
Maintaining transparency throughout implementation supports consistency across the care team.
What the New Standard Means for Your Clinic
The move toward GLI Global race-neutral reference equations reflects an ongoing effort to improve consistency and standardization in pulmonary function testing.
For pulmonologists, the transition reinforces several broader trends:
- Greater reliance on z-scores and Lower Limits of Normal
- Consistent interpretation across diverse patient populations
- Reduced dependence on race-specific adjustment factors
- Increased emphasis on complete pulmonary physiology rather than isolated spirometry values
For pulmonary laboratories, the update also highlights the importance of having technology that supports current standards across the full spectrum of pulmonary function testing.
Practices that perform only spirometry may face limitations when evaluating patients with restrictive disease, complex interstitial lung disorders, or unexplained dyspnea. Complete PFT systems capable of measuring spirometry, lung volumes, and DLCO provide clinicians with the comprehensive physiological data needed for more informed diagnostic decisions.
As respiratory medicine continues to evolve, laboratories equipped with modern software, current reference equations, and comprehensive testing capabilities will be well positioned to deliver consistent, guideline-aligned pulmonary function assessment.
Whether implementing updated GLI Global reference equations for the first time or reviewing existing workflows, adopting race-neutral interpretation is an opportunity to strengthen both diagnostic consistency and clinical confidence across your pulmonary practice.
Conclusion
The adoption of GLI Global reference equations marks a meaningful evolution in pulmonary function interpretation. While the underlying measurements remain unchanged, the move to race-neutral spirometry, greater reliance on z-scores, and consistent application of the Lower Limit of Normal provide a more standardized framework for evaluating lung function across diverse patient populations.
For practices performing complete pulmonary function testing, the transition also underscores the importance of interpreting spirometry, lung volumes, and DLCO together. A comprehensive approach can improve diagnostic clarity, particularly for patients with restrictive lung disease, interstitial lung disease, pulmonary vascular disorders, or complex respiratory presentations.
As laboratories update software, educate staff, and align with current guidance, choosing technology that supports modern reference equations across the full spectrum of pulmonary function testing can help ensure accurate, consistent, and future-ready interpretation.
PulmOne’s MiniBox+ is designed to support this comprehensive approach by providing cabinless, gasless lung volume measurement alongside spirometry and DLCO in a compact platform—helping pulmonary practices deliver complete PFT testing under today’s evolving race-neutral standards.