Validation of predictive equations against DXA for estimation of body fat composition in Vietnamese children
MedPharmRes, 2020, 4
11
MedPharmRes
journal of University of Medicine and Pharmacy at Ho Chi Minh City
Original article
Validation of predictive equations against DXA for estimation of body fat
composition in Vietnamese children
Thanh V. Kima*, Tam M. Doa, Thanh T.K. Trana, Xuan M. Ngob, Hong K. Tanga
aDepartment of Epidemiology, Faculty of Public Health, Pham Ngoc Thach University of Medicine, Ho Chi Minh City
70000, Vietnam;
bPham Ngoc Thach University of Medicine, Ho Chi Minh City 70000, Vietnam.
Received February 05, 2020: Revised March 26, 2020: Accepted April 20, 2020
Abstract: Background: Childhood overweight and obesity are becoming more pronounced in Vietnam, so an
assessment tool of high efficiency in the community is warranted. This study sought to validate skinfold
thickness (SFT) equations for estimation of body fatness by Goran and Slaughter against DXA to aid in
assessing obesity. Method: A cross-sectional study was conducted on 144 healthy children (ages 6-17) who
were conveniently sampled from schools within an urban district. Their anthropometric measurements (height,
weight, and SFT) and DXA whole-body results were taken to record body fat percentage (BF%). Bland-Altman
analysis and correlation between bias and body fat were employed to understand the agreement between results
from each equation and DXA whole body. Result: BF% was 32.2 ± 7.6% (mean ± SD). 52.8% of the children
were overweight or obese. Bland-Altman plots showed that all four SFT equations had wide limits of agreement
(LOAs) and largely underestimated the reference BF% by up to 8.90%. Goran equation predicted better when
BF% decreased, whereas Slaughter equations produced less bias when there was more body fat. Conclusion:
The prevalence rate of overweight and obesity has become alarming. Besides, Goran and Slaughter equations
cannot be used as alternatives for DXA scanning to measure body fat due to their underestimation.
Keywords: Validation; predictive equation; body fat.
1. INTRODUCTION
have been raised about this index’s validity [8, 9]. Hence,
other alternatives have been developed. Until now, the use of
adiposity for diagnosing childhood obesity is increasingly
endorsed by contemporary literature [8-12].
While high-income countries have struggled against
obesity epidemic, countries at lower end of SDI
(socialdemographic index) levels witnessed a significant
increase childhood obesity [1]. Notably in Vietnam, 2014-
2015 surveillance of the National Institute of Nutrition
showed nearly one in two urban children were obese [2]. Once
a child becomes overweight or obese, he or she is more likely
to maintain this condition to adulthood [3, 4]. Furthermore,
this condition may lead to chronic diseases for these children
when they grow up [5-7]. Currently, health professionals most
depend on BMI to diagnose this condition although concerns
DXA is becoming a reference method to measure body fat
[13]. However, due to logistic and financial limitations,
technical complexity and concerns for radiation, it is not
feasible to use DXA widely and routinely on the field.
Therefore, scores of equations using anthropometric
characteristics were developed to estimate body fat
percentage because of the usefulness of these measures in
various settings, especially at the primary care level. In
*Address correspondence to Thanh V. Kim at Department of Epidemiology,
Faculty of Public Health, Pham Ngoc Thach University of Medicine, Ho Chi
DOI: 10.32895/UMP.MPR.4.2.2
© 2020 MedPharmRes
12 MedPharmRes, 2020, Vol. 4, No. 2
Kim et al.
children, they include famous equations developed by
Slaughter or Goran [14, 15]. These predictive equations were
built upon specific populations and need validating on other
populations before being used. So far, to our best knowledge,
little or no previous studies have confirmed the validity of
these equations on Vietnamese children.
performed and analysed by musculoskeletal physicians from
115 People’s hospital, according to hospital standard protocol.
2.5. Statistical analysis
We used the software Stata 14.2 (StataCorp LLC) to
analyse the data. Unpair t-test was performed to compared
continuous data between two genders. To measure the
agreements between predicted and measured body fat, we
plotted the Bland-Altman analysis. Pearson’s correlation was
also performed to assess the change of bias across the average
values of predicted and measured body fat. Correlation
coefficient was categorized into no correlation, weak
correlation, moderate correlation, and strong correlation as
previously described [19].
The present study primarily aimed to validate current
predictive equations against DXA on children from 6 to 17
years of age currently living in Ho Chi Minh city. The
secondary aim was to describe the anthropometric
characteristics of the same population.
2. MATERIALS AND METHOD
2.1. Study design and sample
This cross-sectional study recruited 144 children of
normal health (72 boys and 72 girls) aged 6 – 17. They were
conveniently sampled from 5 schools (2 elementary, 2
secondary and 1 high school) in District 10 of Ho Chi Minh
City during the 2018 – 2019 period. The eligibility criteria
were children from 6 – 17 years of age, not having any acute
or chronic illnesses nor using any medications which were
related to the alteration in body composition.
2.6. Ethics
The study was conducted under the ethic approval from
Pham Ngoc Thach University of Medicine. We gave the
parents a written consent form to sign up for participation after
they were informed of information related to the study.
3. RESULTS
3.1. Participants’ characteristics
2.2. Anthropometric measurements
Data from Table 1 show descriptive data from participants
aged between 6 and 17. More than half were overweight or obese.
Moreover, though boys had significantly lower body fat, more of
them were obese than girls. Nearly half of the children were in
post-puberty.
The research team came to the schools to collect
anthropometric data according to a protocol as previously
described [16]. We took weight and height measurements in
kg and cm, respectively, and to the closest 0.1 unit. Waist size
was taken at the navel level, and hip size was measured at the
largest place at the sagittal plane, both to the closest 0.1 cm.
Then computed BMI was classified using 2007 WHO Child
Growth Standards [17].
3.2. Agreement between predicted and measured BF%
In Table 2, the significant biases between the two methods
show that the four SFT equations underestimated the reference
BF%. The 95% LOAs were wide with the gap fluctuating from
25.50% (Goran’s) to 35.78% (Slaughter’s). Although the bias
from Goran equations was the most pronounced, its LOAs was
the narrowest. Furthermore, the correlation degree between bias
and average BF% from DXA and each equation was weak to
moderate, indicating the bias significantly changed across the
body fat continuum (Figure 1). Specifically, as for the three
Slaughter equations, the more body fat, the lower the bias.
Conversely, the bias from Goran equation became larger when
children had more body fat.
Trained research staff took skinfold thickness (SFT) at 6
sites on the right body parts (triceps, subscapular, abdominal,
supra-iliac, mid-thigh, and medial calf) with Harpenden
Calliper (Baty International, England) to the closest 0.2 mm.
We took two measures at each site, and if the two readings
differed by more than 0.5 cm, recorded the third with the same
method.
Furthermore, the maturational level was first rated in a
medical room by peadiatricians from Children’s Hospital 1
using Tanner staging. After that, the children were grouped
into prepubescent, pubescent and postpubescent based on
WHO recommendation [18].
4. DISCUSSION
2.3. BF% calculation
In this study, we found that Goran and three Slaughter SFT
equations underestimated the BF% measured by DXA scans.
Also, the difference computed by Goran equation was larger
when the child has more body fat. Conversely, with three
Slaughter equations, the difference yielded was larger when a
child has less body fat. Therefore, we cannot use these equations
as a replacement for DXA. We also learnt that the proportion of
children with overweight or obesity had gone up to 52.8%; BF%
was 32.2 ± 7.6 %. As far as we can tell, this is the first study in
Vietnam to validate predictive equations against DXA scans with
the latest nutritional status data from children in Ho Chi Minh
city.
The Slaughter equations, which include ones for Triceps
and Calf (Tri+Calf), ones for Triceps and Subscapular
(Tri+SS) in white and black, were employed to predict BF%
[14]. As for Goran equation, because it produces fat mass in
kilogram, we calculated BF% by dividing predicted fat mass
by weight [15].
2.4. Dual-energy X-ray absorptiometry (DXA)
DXA whole-body scanning was taken to measure BF%
(Hologic Discovery QDR system) at the Department of
Diagnostic Imaging at 115 People’s Hospital. Scans were
Validation of equations for estimating body fat in Vietnamese children
MedPharmRes, 2020, Vol. 4, No. 2 13
Table 1. Descriptive characteristics, by gender
Total
Boys
Girls
Mean±SD/ n (%)
Mean±SD/ n (%)
72 (50 %)
Mean±SD/ n (%)
72 (50 %)
N
144 (100%)
Age (year)
11.7 ± 3.2
12.0 ± 3.3
48.7 ± 17.9
147.8 ± 18.1
73.7 ± 12.0
84.3 ± 12.5
30.0 ± 8.1
11.5 ± 3.1
42.0 ± 13.2*
143.1 ± 14.0
69.6 ± 10.9*
80.3 ± 13.3
34.4 ± 6.3***
Weight (kg)
45.4 ± 16.0
145.5 ± 16,3
71.6 ± 11.6
82.4 ± 13.0
32.2 ± 7.6
Height (cm)
Waist circumference (cm)
Hip circumference (cm)
BF% by DXA (%)
Skinfold thickness
Triceps (mm)
17.2 ± 7.4
14.6 ± 8.2
19.2 ± 11.0
23.2 ± 12.6
23.2 ± 12.8
17.7 ± 9.3
76 (52.8 %)
16.6 ± 6.6
13.7 ± 5.4
19.5 ± 10.0
23.7 ± 12.5
17.7 ± 8.5
13.5 ± 5.5
46 (63.9 %)
17.7 ± 8.2
Sub-scapular (mm)
Abdominal (mm)
Supra-iliac (mm)
Mid-thigh (mm)
Medial Calf (mm)
Overweight - Obesity †
Maturational level
Prepubescent
15.7 ± 10.3***
18.9 ± 11.9
22.6 ± 12.8
28.7 ± 14.1***
21.8 ± 10.5***
30 (41.7 %)**
55 (38.2%)
25 (17.4%)
64 (44.4%)
38 (52.8%)
2 (2.8%)
17 (23.6%)
23 (31.9%)
32 (44.5%)
Pubescent
Postpubescent
32 (44.4%)
* <0.05; ** <0.01; *** <0.001; † WHO 2007
Table 2. Biases and 95% limits of agreement between predicted and measured BF%
Bias (%) 95% Limits of Agreement (%)
95% CI
r
Mean
Lower
Upper
Goran
8.90
7.90 - 10.00
-3.80
21.70
0.44*
Slaughter
(Tri+Calf)
6.02
4.60 - 7.45
-10.90
23.00
-0.31*
Slaughter
5.95
4.50 - 7.40
4.96 - 7.97
-11.70
23.60
24.35
-0.28*
-0.31*
(Tri+SS) Whites
Slaughter
6.46
-11.43
(Tri+SS) Blacks
* p<0.001; Bias: BF% by DXA minuses values from SFT equations; 95% limits of agreement: ± 2 SD of the mean difference
between two methods; r: correlation between bias and average of BF% form two methods. Abbreviation: CI: Confidence Interval;
Tri+Calf: Triceps and Medial Calf; Tri+SS: Triceps and Subscapular.
The first finding is the underestimation of BF% by predicted
equations. This could be explained by the differences in
anthropometric and ethnic characteristics. Firstly, Goran used a
Caucasian sample to develop his equations; Slaughter’s sample
also included Caucasian and Black children [14, 15]. A study by
Deurenberg et al [20] showed that Asian people might have 3–
5% higher body fat compared with Caucasian people with similar
BMIs. This can be because Asian people accumulate a greater
amount of abdominal fat tissue [21]. Secondly, roughly one in
two children in our sample were overweight or obese, while
Goran’s and Slaughter’s development samples were of the
normal weight range. Hence, bias and LOAs would become
wider. In other studies [22-25], the underestimation was also
reported and mean biases ranged from 2.9 to 11.1%. Only
14 MedPharmRes, 2020, Vol. 4, No. 2
Kim et al.
Wickramasinghe et al [26] showed that Slaughter equations for
white children overestimated by 5.9% ± 8.4 (mean bias ±
standard deviation).
The strength of our study is that we used DXA as a reference
method. This technique has high validity and reliability in
measuring BF% [13]. Furthermore, the use of Bland-Altman
analysis was more accurate than merely using correlation or t-test
to evaluate the agreement between two methods. However, we
find it hard to generalize our results because our sample was well-
characterised. Five conveniently-sampled schools were adjacent
to each other and located near the city centre. Also, our sample
was relatively small and could not be representative of children
of Ho Chi Minh city.
The wide LOAs and significant change of bias across the
body fat continuum also described in previous studies [22-26].
These studies shared the same bias trends by Slaughter’s [22-26]
and Goran’s [24, 25]. The correlation was negative between BF%
bias from Slaughter equation and average BF% in children with
excessive fat in Gonzalez-Ruiz’s study and type 1 diabetes
children in Sarnblad’s study [22, 23]. However, in the healthy
group in Samblad’s study and Wickramasinghe et al, no
significant correlation was observed [23, 26].
SFT equations are convenient tools to measure body
composition on the field. Therefore, more and more research has
Figure 1. Comparison of BF% measured by DXA in comparison with Goran and three Slaughter equations,
displayed as Bland-Altman plots.
Y-axis represents bias of BF% measured by DXA minus BF% measured by the equations. X-axis represents
average of BF% measured by DXA and the equations. Central dash lines represent the mean biases between 2
methods. Dotted lines on the either sides represent upper and lower limits of agreement. Solid diagonal lines are
fitted line representing the relationship between biases and average BF% by each pair of methods. Abbreviations:
Tri+Calf: Triceps and Medial Calf; Tri+SS: Triceps and Subscapular; BF%: body fat percentage; DXA: dual
energy X-ray absorptiometry; r: correlation between bias and average of BF% form two methods.
Furthermore, the figure that 52.8% of the children were
overweight or obese might imply the growing trend of
overweight and obesity in urban area. In 2014, Thuy et al [27]
found that the prevalence in urban secondary schools in Hanoi
was 36.2%. Earlier in 2010, the figure in Phuong et al [28] were
27.5% of children from urban secondary schools in Ho Chi Minh
city.
been done to validate predictive equations on a specific
population. Our results raise a need to develop new
anthropometric equations on Vietnamese children. Also, larger-
scaled studies are warranted to determine the nutrition status of
children in urban and in rural schools as well.
5. CONCLUSION
Validation of equations for estimating body fat in Vietnamese children
MedPharmRes, 2020, Vol. 4, No. 2 15
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We found that Slaughter and Goran equations cannot predict
accurately BF% of children in Ho Chi Minh city and the
development of new anthropometric equations is warranted.
Moreover, with the preliminary results showing an alarming
figure ofover 50% of children with overweight or obese, we need
a large-scale study to have a bigger view of the situation.
ACKNOWLEDGEMENTS
General: We would like to send our gratefulness to
Chamber of Education, People Committee District 10;
Administration Committee of Thien Ho Duong Primary
School, Le Thi Rieng Primary School, Tran Phu Junior High
School, Hoang Van Thu Junior High School, Nguyen Du High
School for your cooperation and assistance throughout the
study.
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Funding: This study was supported by Research Fund
provided by Pham Ngoc Thach University of Medicine.
Author Contributions: TK substantially contributes to
conceptual design, acquisition of data, drafting the article; TD
contributes to acquisition of data, data analysis and
interpretation, and revising the article; TT contributes to data
acquisition and data analysis; XN contributes to design the
study, critically revises the article; HT substantially
contributes to study design, critically revises the article,
makes final approval for submission.
Competing interests: The authors declare no conflict of
interest.
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