Systematic misclassification of lung function in Indian adolescents using GLI-2012 reference equations: evidence from...

Accurate spirometric interpretation depends on appropriate reference equations. The Global Lung Function Initiative (GLI-2012) equations are widely used internationally, but South Asian populations were sparsely represented in their derivation and their applicability in Indian adolescents remains uncertain.

We performed a cross-sectional analysis of baseline data from the multicity Air Pollution Exposure on Adolescents' Lungs cohort. Healthy, non-smoking school-going adolescents aged 11-14 years from Delhi, Mumbai, Bengaluru and Mysuru underwent spirometry using standardised American Thoracic Society/European Respiratory Society procedures. GLI-2012 z-scores for forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and FEV₁/FVC were calculated using the Asian reference category. Fit was assessed using mean z-scores and the proportion below the lower limit of normal (LLN; z<-1.645).

Among 4175 adolescents (2148 males), mean z-scores were -2.44 (SD 1.27) for FEV₁, -1.34 (0.93) for FVC and -0.78 (1.11) for FEV₁/FVC, all well outside the accepted ±0.5 range for adequate fit. Overall, 74.6% were below the LLN for FEV₁, 36.8% for FVC and 19.3% for FEV₁/FVC, compared with the expected 5% in a well-calibrated healthy population. The leftward shift in z-score distributions was consistent across sex, city, age, height and body mass index strata.

GLI-2012 equations, as currently applied in the absence of South Asian-specific references, demonstrated substantial calibration mismatch relative to this cohort of Indian adolescents and risk major overclassification of low lung function. Population-specific validation and recalibration are needed before routine clinical or epidemiological use in this population.