Transitioning from Miller to GLI reference equations for DLCO interpretation resulted in a 7.4% discordance rate, with 6.9% of results abnormal by Miller only and 0.5% abnormal by GLI only.
Cross-Sectional (n=63,357)
Yes
Does the use of GLI reference equations compared to Miller reference equations change the interpretation of DLCO results in a pulmonary function laboratory population?
The use of GLI reference equations for DLCO substantially alters interpretation compared to Miller equations, shifting a meaningful subset of patients from abnormal to normal classification.
Absolute Event Rate: 0.5% vs 6.9%
Abstract Background Single breath diffusing capacity of the lung for carbon monoxide (DLCO) remains the most widely used test to assess pulmonary gas exchange. GLI DLCO reference equations are based on a larger, more diverse dataset and offer age-specific and internally consistent reference values. However, their impact on interpretation in a real-world population remains uncertain. Research Question Describe the direction and magnitude of DLCO interpretation changes resulting from our multicenter PFT laboratory transition from Miller to GLI reference equations. Study Design and Methods In this multicenter cross-sectional study, we reanalyzed 88,060 DLCO measurements in a large pulmonary function laboratory database performed between 2016 and 2022 using GLI and Miller reference equations, stratified by self-reported race and ethnicity. Baseline patient characteristics and lung function measurements were summarized with continuous characteristics as median (IQR) and categorical variables as n (%). Kruskal-Wallis test was used to evaluate the difference between GLI and Miller DLCO % predicted difference between races, and two-by-two and four-by-four tables were generated to summarize the proportion of concordance and discordance of GLI to Miller severity levels. A repeated measures multivariable logistic regression was used to evaluate discordance between GLI and Miller severity and patient characteristics (age, sex, race, and BMI). Results We included 63,357 individuals with 88,060 PFT visits; 91.6% (58,076) identified as Caucasian, 5.2% (3,262) as Black, 1.4 % (895) as Asian, and 1.8% (1,113) as mixed/other race. Fifty-one percent were female with an median age of 64 years (range: 5- 85). 7.4% (6509) of DLCO results were discordant, with 0.5% (n = 439) abnormal by GLI only, and 6.9% (n = 6070) abnormal by Miller only. Compared to the Miller, GLI interpretations were associated with a greater shift toward normal interpretations. Younger age, lower BMI, female sex, and being of NE Asian, SE Asian, or Other/mixed race compared to Caucasian were associated with higher odds of discordance in DLCO severity/normal classification. Interpretation The use of GLI reference equations substantially alters the interpretation of DLCO results, shifting a meaningful subset of patients from abnormal to normal classification. While GLI reference equations offer more comprehensive, population-based approach, it is crucial to place these interpretations within the context of the patient presentation until further investigations more clearly define the clinical implications of these transitions. This abstract is funded by: none
Farah et al. (2026) conducted a cross-sectional in Pulmonary function testing (n=63,357). GLI reference equations vs. Miller reference equations was evaluated on Discordance in DLCO severity/normal classification. Transitioning from Miller to GLI reference equations for DLCO interpretation resulted in a 7.4% discordance rate, with 6.9% of results abnormal by Miller only and 0.5% abnormal by GLI only.