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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 2, March/April 2017
94
AFRICA
brand of mercury sphygmomanometer. Systolic (SBP) and
diastolic blood pressure (DBP) were the first and the fifth
koroktoff sounds, respectively. Three consecutive measurements
were made at an interval of five minutes after a 10-minute rest.
The mean SBP and DBP determined from the second and third
measurements were used for data analysis.
Anthropometric indices were calculated as follows:
BMI
=
weight (kg)/height
2
(m); WHR
=
WC (cm)/HC (cm);
WHtR
=
WC (cm)/height (cm); PI
=
weight (kg)/height
3
(cm);
BAI
=
HC (cm)/height
1.5
(m) – 18; CI
=
WC (m)
__________
0.109
×
weight (kg)
_______
height (cm)
Hypertension was defined using the WHO/ISH criteria of
SBP
≥
140 mmHg and/or DBP
≥
90 mmHg, or clinical diagnosis
of hypertension, or prescription of any hypertensive drug.
Prehypertension was defined as SBP
≥
120 mmHg and/or DBP
≥
80 mmHg.
This study was conducted with adherence to ethical standards.
Ethical approval was obtained from the ethics committee of
Nnamadi Azikiwe Uiversity, Awka, Nigeria. The objectives and
nature of the study were duly explained to the participants prior
to the day of the test and interview. Informed consent in written
form or by thumb print was obtained from all participants or
parents. Strict confidentiality was maintained in accordance with
standard medical practices.
Statistical analysis
Comparison of means between the two groups was done using
the independent
t
-test. Poisson regression models were used to
examine the association between anthropometric indices and
hypertension/prehypertension prevalence. The receiver operating
characteristic (ROC) curve analysis was used to compare the
performance of the anthropometric indices as potential predictors
of the disease. The ROC curve is an analytical approach to
define the highest combination of sensitivity and specificity of a
screening test. The approach has been widely used to determine
a cut-off point for decision making (e.g. having a disease or not)
in both public health and clinical settings.
Area under the curve (AUC) was used as a measure of
predictive power. It is the most common measurement to
quantify the performance of a screening test, and shows the
ability of a test to correctly classify those with and without the
disease. For example, an AUC of 0.75 indicates that 75% of the
time, a randomly selected individual from the diseased group has
a test value larger than that for a randomly selected individual
from the non-diseased group. AUC values range from 0.5 (no
prediction) to 1.0 (perfect prediction). AUC values are usually
used as criteria to compare overall performance of different
screening tests. In this study, AUCs for models were estimated
using logistic regression models.
To determine if the inclusion of WC, WHtR or PI improved
the prediction of hypertension using BMI, we estimated the
change in gender-specific prevalence ratio (from Poisson
Table 1. General characteristics of the study population
Variables
No hypertension,
n
(%)
Hypertension,
n
(%)
Age (years)
≤ 20
92 (10.09)
7 (0.77)
21–25
279 (30.59)
29 (3.18)
26–40
245 (26.86)
90 (9.87)
≥
41
88 (9.65)
82 (8.99)
City
Awka
241 (26.43)
59 (6.47)
Onitsha
203 (22.26)
98 (10.75)
Nnewi
260 (28.51)
51 (5.59)
Gender
Male
340 (37.28)
96 (10.53)
Female
364 (39.91)
112 (12.28)
Body mass index
Underweight
13 (1.43)
3 (0.33)
Normal weight
394 (43.20)
64 (7.02)
Overweight
219 (24.01)
92 (10.09)
Obese
78 (8.55)
49 (5.37)
Smoking
No
683 (75.64)
192 (21.26)
Yes
15 (1.66)
13 (1.44)
Physical activity
Not active
25 (2.75)
31 (3.41)
Moderately active
385 (42.35)
136 (14.96)
Active
292 (32.12)
40 (4.40)
Alcohol consumption
Not at all
314 (35.01)
89 (9.92)
≤ 1 per month
265 (29.54)
51 (5.69)
1–3 times per week
83 (9.25)
36 (4.01)
Every day
31 (3.46)
28 (3.12)
Table 2. Mean (SEM) values of the anthropometric indices categorised by gender and hypertension status
Male
Female
p-value
Normal
(
n
=
142)
Prehypertensive
(
n
=
198)
Hypertensive
(
n
=
96)
Normal
(
n
=
174)
Prehypertensive
(
n
=
192)
Hypertensive
(
n
=
112)
SBP,
n
(%)
104.44 ( 6.51)
121.29 (7.94)
145.13 (16.36)
104.44 (6.51)
121.54 (7.48)
145.68 (15.95)
0.749
DBP,
n
(%)
68.41 (6.02)
77.79 (5.39)
96.05 (8.98)
68.41 (6.02)
78.37 (5.94)
93.42 (11.32)
0.8795
Weight,
n
(%)
66.30 (9.10)
72.28 (11.13)
77.97 (14.09)
64.72 (11.11)
69.45 (11.86)
72.98 (15.55)
0.0000
Height,
n
(%)
169.11 (7.69)
169.74 (7.25)
170.58 (7.48)
162.20 (7.34)
162.50 (7.07)
162.65 (7.14)
0.0000
WC,
n
(%)
83.48 (8.03)
87.99 (8.16)
93.64 (11.86)
86.32 (10.66)
90.39 (12.71)
93.40 (11.86)
0.0117
HC,
n
(%)
93.56 (9.12)
97.58 (8.70)
101.73 (12.73)
98.08 (12.76)
101.09 (12.89)
103.58 (13.23)
0.0000
WHR,
n
(%)
0.89 (0.067)
0.90 (0.04)
0.92 (0.04)
0.88 (0.07)
0.90 (0.06)
0.90 (0.05)
0.0028
WHtR,
n
(%)
0.49 (0.044)
0.55 (0.067)
0.22 (0.03)
0.21 (0.03)
0.22 (0 .03)
0.23 (0.03)
0.0000
PI,
n
(%)
13.75 (1.96)
14.85 (2.49)
15.69 (2.37)
15.17 (2.33)
16.28 (3.07)
16.94 (3.28)
0.0000
BAI,
n
(%)
24.57 (3.91)
26.24 (4.56)
27.68 (5.33)
29.54 (5.96)
30.96 (6.97)
31.99 (6.19)
0.0000
BMI,
n
(%)
23.18 ( 2.90)
25.12 (3.78)
26.72 (3.95)
24.55 (3.57)
26.34 (4.43)
27.51 (5.22)
0.0001
CI,
n
(%)
1.23 (0.11)
1.24 (0.09)
1.28 (0.13)
1.25 (0.10)
1.27 (0.13)
1.29 (0.10)
0.0007
SBP, systolic blood pressure; DBP, diastolic blood pressure; WC, waist circumference; HC, hip circumference; WHR, waist–hip ratio; WHtR, waist–height ratio; PI,
ponderal index; BAI, body adiposity index; BMI, body mass index; CI, conicity index.