CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 4, July/August 2011
AFRICA
209
Blood pressure was taken by connecting subjects to the
Finapres (finger arterial pressure) apparatus.
15
Details of how
this procedure was conducted are described elsewhere.
16
High
blood pressure was defined according to the definition from
the National High Blood Pressure Education Program work-
ing group on high blood pressure in children and adolescents
(2004),
17
i.e. an average systolic or diastolic blood pressure
>
95th percentile for gender, age and height.
SAS statistical package version 9.0 (2003)
18
was used for data
analysis. Descriptive statistics were computed by gender for age,
height, weight, BMI, WC, WHtR, systolic blood pressure (SBP),
diastolic blood pressure (DBP) and percentage body fat (% BF),
expressed as mean and standard deviation (SD). Differences
among means were investigated by analysis of variance.
Diagnostic accuracy of WHtR to predict high blood pressure
was expressed in the following ways: sensitivity and specific-
ity, odds ratio and confidence interval, positive predictive value
(PPV) and negative predictive value (NPV). Sensitivity meas-
ures are the proportion of actual positives which are correctly
identified as such, and specificity measures are the proportion
of negatives which are correctly identified. The optimal cut-off
value was denoted by the value that had the largest overlap of
sensitivity and specificity.
19
The odds ratio compares the prob-
ability of a certain event for two groups. The PPV of a test is
the probability that a patient has a positive outcome given that
they have a positive test result. This is in contrast to sensitivity,
which is the probability that a patient has a positive test result
given that they have a positive outcome. Similarly, the NPV is the
probability that a patient has a negative outcome given that they
have a negative test result, in contrast to specificity, which is the
probability that a patient has a negative test result given that they
have a negative outcome.
20
Results and Discussion
Characteristics of the children are presented in Table 1. Girls had
statistically significantly greater values for all variables except
for age, weight and WHtR. The prevalence of abdominal adipos-
ity using a WHtR cut-off value of 0.5 identified 7.9% of the girls
and 3.4% boys as having excess central adiposity. Overall, the
prevalence of hypertension in these children was 13%.
Table 2 shows the comparison between the South African
children in this study and a sample of children aged six to 14
years from a Japanese study, which was aimed at determining
the best predictor for the presence of cardiovascular disease risk
factors among anthropometric indices.
4
The average value of
WHtR in these children was between 0.41 and 0.44. Based on the
results obtained, the authors proposed that WHtR could be used
for detecting cardiovascular risk in children.
Tables 3 and 4 show different frequencies of children in each
category of true positives, false positives, false negatives and
true negatives which were used in the calculation of positive and
negative predictive values for WHtR as a predictor of high blood
pressure. The results obtained for different diagnostic measures
TABLE 1. MEANAND STANDARD DEVIATION FOR THE
CHARACTERISTICS OF THE CHILDREN
Variable
Boys
Girls
p
-value
Age (years)
12 (1.7)
12 (1.7)
0.91
Height (cm)
147.8 (13.0) 148.8 (11.1)
<
0.01
Weight (kg)
38.0 (11.6) 41.0 (11.7)
0.18
Body mass index (kg/m
2
)
17.0 (3.1)
18.2 (3.5)
<
0.01
Waist circumference (cm)
60.7 (7.4)
61.7 (7.8)
0.03
Waist-height ratio
0.41 (0.04) 0.41 (0.04)
0.13
Systolic blood pressure (mmHg) 99.21 (14.0) 104.3 (14.2)
<
0.01
Diastolic blood pressure (mmHg) 63.8 (9.7)
65.5 (9.5)
<
0.01
% body fat
14.4 (6.2)
22.8 (6.9)
<
0.01
TABLE 2. MEANAND STANDARD DEVIATION FOR
THE CHARACTERISTICS OF JAPANESE
AND SOUTHAFRICAN CHILDREN
Variable
South African
Japanese
Boys
Girls
Boys
Girls
Age (years)
12.0 (1.7)
12.0 (1.7)
10.9 (0.5) 10.9 (0.5)
Height (cm)
147.8 (13.0) 148.8 (11.1) 145.2 (7.2) 144.4 (6.4)
Weight (kg)
38.0 (11.6) 41.0 (11.7) 39.2 (8.9) 38.3 (7.3)
Body mass index
(kg/m
2
)
17.0 (3.1)
18.2 (3.5)
18.4 (3.0) 18.0 (3.2)
Waist circum-
ference (cm)
60.7 (7.4)
61.7 (7.8)
61.2 (7.9) 58.1 (6.4)
Waist-height ratio 0.41 (0.04) 0.41 (0.04) 0.43 (0.05) 0.40 (0.04)
Systolic blood
pressure (mmHg)
99.21 (14.0) 104.3 (14.2) 113.8 (11.2) 99.2 (14.0)
Diastolic blood
pressure (mmHg)
63.8 (9.7)
65.5 (9.5)
60.4 (7.6) 61.5 (7.3)
% body fat
14.4 (6.2)
22.8 (6.9)
20.0 (8.0) 24.0 (7.0)
TABLE 5. DIAGNOSTICACCURACY MEASURES FORWHTR
ASA PREDICTOR OF BLOOD PRESSURE FOR BOYSAND
GIRLSAT 0.41 AND 0.5WC CUT-OFFVALUES
Diagnostic accuracy
measures
Waist circumference cut-off values
Boys
Girls
0.41
0.5
0.41
0.5
Sensitivity (%)
61.9
4.8
62.0
7.6
Specificity (%)
53.6
98.6
51.4
93.9
Positive predictive
value
0.53
0.99
0.51
0.97
Negative predictive
value
0.38
0.95
0.39
0.92
Odds ratio
1.88
3.45
1.63
3.09
95% confidence
interval
0.97; 3.67 0.61; 19.37 0.97; 2.74 1.04; 9.20
Table 3. 2
×
2 table for boysat 0.41 and 0.5waist
circumference cut-offvalues
WHtR
≤
0.41
WHtR
≥
0.41 Total
WHtR
≤
0.5
WHtR
≥
0.5 Total
Non-hypertensive 150
129 279 276
4 280
Hypertensive
16
26 42 40
2
42
Total
166
155 321 316
6 322
Table 4. 2
×
2 table for girlsat 0.41 and 0.5waist
circumference cut-offvalues
WHtR
≤
0.41
WHtR
≥
0.41 Total
WHtR
≤
0.5
WHtR
≥
0.5 Total
Non-hypertensive 148
144 292 284
8 292
Hypertensive
29
46 75 69
6
75
Total
177
190 367 353 14 367
