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].