Reference equations for evaluation of spirometry function tests in South Asia, and amongst south asians living in other countries

Abstract

Background: There is little data to accurate interpretation of spirometry data in South Asia, a major global region with high reported burden for chronic respiratory disease. Method: We measured lung function in 7,453 healthy men and women aged over 18 years, from Bangladesh, North India, South India, Pakistan and Sri Lanka, as part of the South Asia Biobank study. We first assessed the accuracy of existing equations for predicting normal forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and FEV1/FVC ratio. We then used our data to derive (N=5589) and internally validate (N=1864) new prediction equations amongst South Asians, with further external validation amongst 339 healthy South Asians living in Singapore. Results: GLI2012 and NHANESIII consistently overestimated expiratory volumes (best fit GLI-African American, mean [sd] z-score (n=7453): FEV1 -0.94 [1.05]; FVC -0.91 [1.10]). Age, height and weight were strong predictors of lung function in our participants (p<0.001), and sex specific reference equations using these three variables were highly accurate in both internal validation (z-scores: FEV1 0.03 [0.99]; FVC 0.04 [0.97]; FEV1/FVC -0.03 [0.99]) and external validation (z-scores: FEV1 0.31 [0.99]; FVC 0.24 [0.97]; FEV1/FVC 0.16 [0.91]). Further adjustment for study regions improves the model fit, with highest accuracy for estimation of region specific lung function in South Asia. Conclusion: We present improved equations for predicting lung function in South Asians. These offer the opportunity to enhance diagnosis and management of acute and chronic lung diseases in this major global population.