Reference Equations
Normal reference values are critically important for interpreting the results of pulmonary function tests (PFTs), but data in non-White populations are lacking. Several reports in PediatricPulmonology this past year sought to fill this knowledge gap. Al Querem et al. evaluated the applicability of the 2012 Global Lungs Initiative (GLI) reference equations in 582 Jordanian children ages 6-13 year-old [14]. The GLI equation for Caucasians demonstrated a reasonable fit to the data collected in this study and was more suitable than the GLI equation for other ethnic groups, and equations derived from other studies conducted in Arabic counties. These results differ from previously reported values in Jordanian adults which showed that the GLI equations for other ethnicities rather than GLI Caucasian equation were better correlated, and demonstrate the importance of identifying age-specific reference equations.
Reference values for infant PFT’s have been reported but there is a lack of information about racial or ethnic differences. The aim of a study by Kosma et al was to estimate the extent to which previously published reference equations for infant spirometry could be implemented in a cohort of Swedish term, healthy infants [15]. Tidal volume and raised volume rapid thoracoabdominal compression (RVRTC) maneuvers were performed on 91 term infants. Height and weight in Swedish infants were above average compared to other infant PFT reference cohorts, and this led to an underestimation of lung function measured by infant spirometry in the youngest age group and an overestimation in the older infants using previously published infant PFT reference data.
Not only spirometry reference values but also reference equations to calculate diffusing capacity of carbon monoxide (DLCO) have been tested for their applicability in different racial groups. A study by Dridi et al. measured nitric oxide/carbon monoxide transfer in 118 healthy Tunisian males ages 8-14 [16]. They confirmed previous observations that height and body weight are key individual predictors of DLCO and that alveolar volume (VA) was related with both height and weight. Their values for DLCO and VA were similar to those found by Kim et al in both Caucasian and African American populations [17].
Normal reference data for maximal voluntary ventilation (MVV) in children have only been reported for limited ethnic and racial populations. Silva et al. obtained MVV data from children in São Paolo, Brazil [18]. MVV in their cohort differed from results obtained in other populations, highlighting the need and importance to obtain normal reference data for multiple different populations.
Although not the focus of studies published in PediatricPulmonology in 2020, the issue of incorporating race into PFT reference equations has grown in prominence and importance in the past few years. Although genetic ancestry contributes to differences in PFT values in different populations, race is a complex construct that incorporates more than just genetic ancestry, and includes cultural and social factors [19]. Furthermore, race serves as a proxy for social determinants of health that may affect lung function. It is likely that in the future, we will see studies in PediatricPulmonology that more directly incorporate genetic ancestry into predictive equations rather than phenotypic race [20].