Comparison of race-specific and race-neutral GLI spirometric reference equations with an Indian reference equation

Background

Despite the increasing popularity and use of Global Lung Function Initiative (GLI) spirometric reference equations, the appropriateness of the race-specific and race-neutral GLI spirometric reference models among the Indian population has not been systematically investigated.

Methods

In this cross-sectional analysis, we used spirometric measurements of 1123 healthy Indian adults (≥18 years of age). We computed reference values and z-scores for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), and FEV₁/FVC from race-specific and race-neutral GLI reference equations as well as from a widely used Indian reference equation. We studied heterogeneity between GLI equations and the Indian equations using Bland-Altman analysis, and the differences between the reference and observed values were compared using the Friedman test.

Results

In Bland-Altman analysis, significant heterogeneity in FVC and FEV₁ between race-specific and Indian equations was observed (bias: 10.4 % and 14.1 %, respectively), with less bias for FEV₁/FVC (3.76 %). The race-neutral equations showed almost similar bias (9.8 %, 13.8 %, and 3.8 % for FVC, FEV₁, and FEV₁/FVC, respectively). Median differences in race-specific reference values from observed values for FVC and FEV₁ were 0.49L and 0.44L, respectively, decreasing slightly with race-neutral equations (0.46L and 0.43L) whereas Indian models showed minimal differences (FVC: 0.10L, FEV₁: 0.05L). Z-scores for FVC and FEV₁ were significantly different between race-specific and race-neutral GLI equations, and both differed from Indian equations.

Conclusion

Both race-specific and race-neutral GLI reference equations are significantly different from the Indian equations, which underscores the importance of determining the suitability of global reference models before being used indiscriminately.