Validation of the global lung initiative 2012 multi-ethnic spirometric reference equations in healthy urban Zimbabwean 7-13 year-old school children: a cross-sectional observational study

Background The 2012 Global Lung Function Initiative (GLI(2012)) provide multi-ethnic spirometric reference equations (SRE) for the 3-95 year-old age range, but Sub-Saharan African populations are not represented. This study aimed to evaluate the fit of the African-American GLI(2012) SRE to a population of healthy urban and peri-urban Zimbabwean school-going children (7-13 years). Methods Spirometry and anthropometry were performed on black-Zimbabwean children recruited from three primary schools in urban and peri-urban Harare, with informed consent and assent. Individuals with a history or current symptoms of respiratory disease or with a body mass index-z score (BMI) < - 2 were excluded. Spirometry z-scores were generated from African-American GLI(2012) SRE, which adjust for age, sex, ethnicity and height, after considering all GLI(2012) modules. Anthropometry z-scores were generated using the British (1990) reference equations which adjust for age and sex. The African-American GLI(2012) z-score distribution for the four spirometry measurements (FVC, FEV1, FEV1/FVC and MMEF) were evaluated across age, height, BMI and school (as a proxy for socioeconomic status) to assess for bias. Comparisons between the African-American GLI(2012) SRE and Polgar equations (currently adopted in Zimbabwe) on the percent-predicted derived values were also performed. Results The validation dataset contained acceptable spirometry data from 712 children (344 girls, mean age: 10.5 years (SD 1.81)). The spirometry z-scores were reasonably normally distributed, with all means lower than zero but within the range of +/- 0.5, indicating a good fit to the African-American GLI(2012) SRE. The African-American GLI(2012) SRE produced z-scores closest to a normal distribution. Z-scores of girls deviated more than boys. Weak correlations (Pearson's correlation coefficient < 0.2) were observed between spirometry and anthropometry z-scores, and scatterplots demonstrated no systematic bias associated with age, height, BMI or socioeconomic status. The African-American GLI(2012) SRE provided a better fit for Zimbabwean paediatric spirometry data than Polgar equations. Conclusion The use of African-American GLI(2012) SRE in this population could help in the interpretation of pulmonary function tests.