ORIGINAL

Niger J Paed 2014; 41 (3):223 –228

Sadoh WE

Omuemu VO

Sadoh AE

Iduoriyekemwen NJ

Nwaneri UD

Adigweme IN

Owobo AC

Blood pressure percentiles in a

group of Nigerian school age

children

Uduebor JO

Ekpebe PA

DOI:http://dx.doi.org/10.4314/njp.v41i3,14

Accepted: 6th April 2014

Abstract: Background: Determi-

nation of abnormal blood pressure

BP) in children is dependent on

comparison with normal percentile

values. The commonly used Na-

tional Institute of Health (NIH)

standard is generated from children

outside of Africa.

readings were taken. Hypertension

was defined as_t_hsystolic and or dia-

stolic BP >95 percentile of the

study population.

(

)

Sadoh WE

(

Sadoh AE, Iduoriyekemwen NJ,

Adigweme IN, Uduebor JO, Ekpebe PA

Nwaneri UD

Results: There were 1549 subjects,

aged 5 to 15 years, of which 757

(48.9%) were males. Prevalence of

hypertension was 2.6%. Only age

and weight were independent pre-

dictors of both elevated systolic

Department of Child Health,

Omuemu VO

Department of Community Health

University of Benin Teaching Hospital,

PMB 1111, Benin City, Nigeria.

Email: sadohehi@yahoo.com

Objective: To develop BP percen-

tile values for Nigerian children

based on BP cuff width 40% to

th

and diastolic BP. The 5 , 10 , 50 ,

th

5

0% of arm circumference.

90 and 95 percentiles of Systolic

and diastolic BP were generated

for both males and females pupils.

Conclusion: BP Percentiles have

been generated using BP cuff

width 40 to 50% of the arm cir-

cumference for Nigerian children.

Methods: Subjects were pupils

from nine primary schools in Mid-

western Nigeria recruited using a

multi-stage sampling technique.

Their BP was measured using a

cuff width of 40 to 50% of arm

circumference and cuff length of at

least 80% of arm circumference

respectively. The mean of two BP

Owobo AC

Department of Paediatrics,

Irrua specialist Teaching Hospital,

Irrua, Nigeria

Keyword: Blood pressure; hyper-

tension; childhood; percentile

Introduction

and management.

Childhood blood pressure (BP) is an important clinical

parameter of the wellbeing of the child thus, it is impor-

tant to routinely measure BP of children in clinical set-

Hypertension in children according to the Fourth Task-

force on hypertension in children and adolescents is

1

defined as elevated systolic blood pressure (SBP) and or

1

th

tings . Childhood BP has been shown by several work-

diastolic blood pressure (DBP) > 95 percentile for the

ers to be strongly correlated with weight, hei_-g₄ht, body

age and sex. Childhood hypertension is mostly secon-

dary to underlying conditions while a smaller proportion

1

mass index and other anthropometric indices . Higher

9

BP has also been demonstrated in male compared to

is reported to be primary or essential hypertension .

1

-4

9

female children in previous works . This has largely

been related to the weight of the boys being higher than

that of the girls. Some workers have shown higher BP in

urban children compared to the rural children as well as

differences in blood pressure based on socioeconomic

Childhood essential hypertension is on the rise globally ,

it is reported to be associated with family history of es-

sential hypertension and childhood overweight/ obe-

1

0

sity . Decreased physical activity, increase in sedentary

life style including watching television and the large

consumption of the fattening fast food are found to be

5

,6

classes in adolescent girls .

1

contributors to childhood hypertension .

It is important to measure BP in children and identify

those with elevated BP because BP tracks from child-

hood to adulthood . Children with elevated BP tend to

continue to have high BP into adulthood. Thus identifi-

cation of these individuals is important for follow up

The increasing recognition of these facts should per-

suade health care worker as to the need to routinely

measure the BP of children as they present in clinical

and other settings. It is also important to be able to

7

,8

2

24

interpret the measured BP. Interpretation of measured

BP is usually based on comparison of the measured

value with what is considered normal or standard values.

The BP standards generated by NIH and the Nation₁_,a₁₂l

High Blood Pressure Education Program (NHBPEP)

from data obtained from Caucasian, African American,

latino and Asian children would seem ideal for most

children globally and it is currently being used. How-

ever negroid children from Africa were not included in

the data base. The African American children may not

adequately represent the African children since they may

be exposed to different stressors as their environments

are different. In addition, the method of measuring BP

from which the NIH BP standards were derived is

flawed. Cuff specification that include bladder width

that is 40 - 50% of mid arm circumference and bladder

length that is 80 – 100% of the mid arm circumference

will produce a more accurate measurement of BP than

the previous specification that included the cuff width of

19 private schools in the three selected wards from

which 30% each of private and public schools were se-

lected from a list of alphabetically arranged schools.

Thus, three public and six private schools were selected

using a systematic sampling technique after randomly

selecting the first school (second stage). The school

sample size was determined as the ratio of the product of

index school population and study sample size (1549)

over the pooled population of the nine selected schools.

The school sample size was thus determined in propor-

tion to school population. A systematic sampling

method was employed to select pupils from each school.

Evaluation of selected pupils

An informed written consent was obtained from the par-

ents of each selected pupil. Any child whose parent de-

clined to give consent was replaced by the next pupil on

the sampling list selected using the sampling interval

and whose parent gave consent. A socioeconomic class

was ascribed to each selected pupil using the method

2

/3 or 3/4 of the arm’s length, the specification with

10

which the NIH standards were derived . The cuff speci-

fication has been corrected by the steering committee of

America Heart association (AHA) in recommending

cuff size that included bladder width and length that is

1

7

described by Olusanya et al . The selected pupil then

had a thorough general and systemic examination with

emphasis on the cardiovascular system. The weight was

measured with the shoes, wrist watches, belts and other

thick clothing taken off and the subject was in his or her

school uniform only. The Omron body composition

monitor (BF511Netherlands) was employed to measure

the weight. The pupils were instructed to stand erect and

looking straight ahead on the weighing machine. The

weight once captured was displayed on the machine.

The weight was read to the nearest 0.1 kg. The height

was taken with the aid of a stadiometer with the pupils’

shoes and stockings off, the pupils were instructed to

stand against the stadiometer with the heels, buttocks

and occiput resting against the stadiometer. The chin

was raised so that the subject was looking ahead with

the upper border of the ear canal in the same horizontal

plane as the lower border of their eye socket (Frankfurt

plane). The height was read to the nearest 0.1 cm. The

Body Mass Index (BMI) for age was then computed for

the pupils as the ratio of the weight in kg/ square of the

4

cumference for children, in 1988 .This specification

0 - 50% and 80 – 100% respectively of mid arm cir-

13

was also recommended by the 1996 update of₄the Task

1

Force on Blood Pressure Control in Children and the

1

2

NHBPEP . Previous Nigerian studies on childhood

hypertension have relied on the NIH standards which are

now considered flawed. This indicates the need for ap-

propriate standards.

In this study, we set out to determine the BP pattern of a

population of Nigerian primary school pupils aged 5 –

1

5 years and derive BP percentiles based on the new

cuff specification.

Subjects and Methods

2

This cross sectional study was conducted in Egor Local

Government Area (LGA), of Edo state of Nigeria as part

of a larger study to evaluate cardiovascular risks in chil-

dren. The LGA has an estimated total population of

height in metres (m ).

The blood pressure was measured in the right upper arm,

except where there was an injury to the arm (one pupil).

The pupils were made to sit down and relax for about 3

15

39,899 of which 119,038 are aged less than 15 years .

3

1

It is predominantly urban with ten political wards of

which two are rural. This study was conducted over a

six months period (September 2011 to February 2012).

This period included the times the schools were in ses-

sion. Ethical approval for this study was obtained from

the Ethics Committee of the University of Benin Teach-

ing Hospital, Benin City.

minutes before the BP was measured. An appropriate

sized cuff, with bladder width of about 40 - 50% of the

arm circumference and the bladder length of at least

1

80% of the arm circumference was utilised . The cuff

was smugly applied to the right upper arm and the cuff

inflated to about 10 mmHg above the systolic BP by

palpation. The bell of the stethoscope was then applied

over the brachial artery as the cuff was slowly deflated

1

Sampling technique

at a rate of 2mm per second . The first Korotkov sound

was taken as the systolic BP while the fifth Korotkov

sound represented the diastolic BP. Two BP readings

were taken three minutes apart and the average was

taken as the patient’s BP. H_t_hypertension was defined as

elevated SBP or DBP >95 percentile for the age and

sex of the percentiles derived in this study.

One thousand, five hundred and forty nine pupils were

selected using a multi stage sampling technique. Of the

1

0 political wards, 30% (3) of the wards were randomly

selected from a list of the political wards as the first

1

6

stage of the sampling process . There were 8 public and

2

25

Statistical analysis

Blood pressure of the study population

The data was entered into SPSS version 16 (Chicago IL)

spread sheet and analysis done with the same tool. The

prevalence of elevated blood pressure was presented in

percentage. Differences in means of systolic and

diastolic blood pressures were compared using student’s

t test. More than two means were compared using

one-way ANOVA with Turkey-Kramer post hoc test

when significant. Correlation between two continuous

variables was tested using Pearson’s correlation test.

Multiple logistic models were made for predictors of

elevated systolic and diastolic BP. Level of significance

was set at p = <0.05.

Table 3 shows the mean systolic blood pressure (MSBP)

and mean diastolic blood pressure (MDBP) by gender of

the pupils and by age. The MSBP of the male pupils

rose with age from 92.1 ± 6.1 mmHg for the 5 year old

to 113.1 ± 7.4 mmHg for the 15 year old. The difference

in MSBP of the youngest and the oldest was statistically

significant, p = <0.0001. Similarly, the MSBP of the

females rose with age from 91.5 ± 11.2 mmHg in the

five year olds to 119.0 ± 10.2 mmHg in the 15 year olds.

The difference in MSBP between the youngest and old-

est was significant, p = <0.0001. The Mean diastolic

blood pressure (MDBP) of the males rose with age from

5

1

9.0 ± 9.2 mmHg at 5 year to 73.9 ± 10.4 mmHg in the

5 year old. The difference in MDBP of the youngest

and oldest was significant, P = 0.0001. The females

similarly showed a rise in MDBP with age, the differ-

ence was significant, P = 0.001.

Results

Characteristics of the study population

There were 1549 primary school pupils who were re-

cruited for the study. They consisted of 757(48.9%)

males and 792 (51.1%) females. The age range was 5

to15 years with a mean age of 8.8 ± 2.2 years. The mean

age of the female pupils 8.8 ± 2.2 years was not signifi-

cantly lower than the male pupils 9.1 ± 2.2 years, p

There were 41pupils with elevated SBP and / DBP

values >95 percentile for age and sex. The prevalence

of hypertension was thus 2.6%. Of the 41 pupils, 20

(48.78%) were female and 21(51.22%) males. The

prevalence of hypertension among the male and female

pupils were 20/792(2.5%) and 21/757(2.7%)

th

=

0.092. There were 850(54.9%) and 699(45.1%) pupils

from the public and private schools respectively. 1510

pupils had information to compute their SEC. Of the

th

Table 3: The gender 5 , 10 , 25 , 50 , 75 , 90 and 95

height percentiles of the study population

Age _t_h Ma_t_hle Per_t_hcentil_t_hes (in_t_hcm)

1

510 pupils, most 740(49%) were in the low SEC. The

F_te_hmale P_t_hercen_tt_hile (_t_hin cm)

th

5 10 25 50 75 90 95

characteristics of the study population are shown in

table 1.

th

(

yr)

5

10

25 50 75

90 95

5

6

7

8

9

1

109 110 111 115 119 125 127 110 111 114 116 118 121 126

107 112 116 120 123 128 130 110 112 115 120 125 128 130

113 115 120 126 130 134 136 113 116 119 123 128 133 138

116 119 122 127 135 141 143 116 118 122 127 133 138 140

118 120 125 130 137 142 144 118 121 124 130 136 143 144

118 120 127 133 139 142 145 120 124 128 134 139 144 149

Table 1:The characteristics of the study population

Characteristics

Number

Percentage

0

Gender

Male

Female

Type of school

Public

11 121 125 130 134 140 144 146 124 126 131 136 142 147 151

12 124 127 131 136 143 147 149 126 128 133 137 147 152 157

757

792

48.9

51.1

13

14

15

125 128 134 141 146 151 153 133 137 140 143 152 157 159

135 136 136 143 147 152 157 137 140 143 146 153 161 163

132 133 139 151 152 155 159 140 142 145 149 154 164 167

850

699

54.9

45.1

yr = years; cm = centimeters

Private

Socioeconomic class

High

Middle

th

The 5 , 10 , 50 , 90 and 95 percentiles of the SBP

and DBP of the pupils according to age and gender are

shown in figures 1, 2, 3 and 4. The age, weight, height,

BMI were positively correlated with the SBP r = 0.32; P

491

279

740

32.5

18.5

49.0

Low

The height percentiles of the study population

=

0.0001, r = 0.4; P = 0.0001, r = 0.36; P = 0.0001 and r

th

= 0.3; P = 0.0001 respectively. Multiple linear regres-

sions models showed that only age and weight were

independent predictors of elevated SBP; P = 0.0001 and

Table 2 shows the male and female 5 , 10 , 25 , 50 ,

7

lation.

th th th

5 , 90 , and 95 height percentiles of the study popu-

0

.013 respectively. (Table 4) Similarly only age and

weight were independent predictors of elevated DBP; P

0.01 and 0.006 respectively. (Table 5) The age,

Table 2: The mean weight of the pupils by age and gender

=

Age

FEMALE

MALE

FEMALE

year) Weight (Kg) Weight (Kg) P values Height (cm) Height (cm) P value

MALE

weight, height and BMI were positively correlated with

DBP r = 0.29; P = 0.002, r = 0.36; P = 0.0001, r = 0.030

and P = 0.0001, r = 0.26; P = 0.0001 respectively.

(

5

20.1 ± 2.3

22.1 ± 5.2

24.1 ± 5.2

25.4 ± 4.7

30.4 ± 8.4

31.8 ± 7.3

34.1 ± 8.3

36.5 ± 6.3

41.7 ± 7.8

42.3 ± 4.7

49.9 ± 1.1

19.9 ± 3.0

22.0 ± 4.3

25.4 ± 6.4

27.3 ± 6.7

29.1 ± 6.1

30.6 ± 7.9

31.0 ± 5.3

32.3 ± 5.6

36.0 ± 6.6

36.6 ± 2.2

41.6 ± 8.5

0.71

0.94

0.16

0.002

0.15

0.23

116.2 4.0

120.7 6.2

124.6 7.9

115.7 4.9

119.7 6.9

126.7 6.9

0.91

0.30

0.052

0.08

0.92

0.07

0.01

6

7

8

9

1

127.2 12.7 129.6 8.0

131.2 8.4

134.1 8.4

136.7 7.8

139.7 9.6

146.4 7.8

147.8 6.0

150.5 5.2

131.3 8.7

132.1 8.5

133.6 7.1

136.6 7.7 0.04

142.2 9.8

142.9 5.6

0

1

2

3

4

5

0.01

0.001

0.003

0.006

0.04

0.06

0.10

149.8 11.5 0.89

2

26

Table 4: Multiple linear regression model showing independ-

ent predictors of elevated systolic blood pressure

Discussion

Variable Beta Std Error t value P value Confidence Interval

The BP percentile generated in this study was from BP

values obtained as the means of at least two BP readings

using an appropriate cuff based on the circumference of

the arm rather than the length of the a₁rm as recom-

mended by the working Group, NHBPEP .

Constant 65.15 9.2

7.09 0.0001 47.10 – 83.20

3.68 0.0001 0.27 – 0.9

Age

0.59 0.16

0.39 0.16

Weight

Height

BMI

2.74 0.013

0.08 – 0.70

-0.05 – 0.23

-0.39 – 0.76

0.09 0.071 1.22 0.22

0.18 0.30 0.63 0.53

The percentile values generated in this study were based

on only the age of the child which makes it easy to use

in a busy paediatric clinic. The NIH percentiles which is

based on age and the height percentiles of the children is

rather difficult to use, besides in the San Anthonio blood

pressure study, it was shown that the contribution of

height to BP is negligible when weight and age are con-

trolled for. Thus the rationale for the inclusion of height

Table 5: Multiple linear regression model showing

independent predictors of elevated diastolic blood pressure

Variable Beta Std Error t

P value Confidence Interval

Constant 46.7 7.61 6.14 0.0001 31.78 - 61.64

Age

0.45 0.13

0.36 0.13

0.012 0.06

-0.91 0.24

3.40 0.01

2.74 0.006

0.20 0.84

-0.38 0.71

0.19 – 0.71

0.10 – 0.62

-0.10 – 0.13

-0.57 – 0.39

Weight

Height

BMI

1

8

percentiles to childhood BP measurement was queried .

The current NIH BP standard that is in use is limited in

that some of the data used were single BP readings, ob-

tained by using cuff measurement based on the length of

the arm (two thirds or three quarters) which are consid-

ered incorrect by American Heart Academy and the

th

Fig 1: The 5 , 10 , 50 ,

9

th th

0 and 95 percentiles

of the male systolic

blood pressure

1

working group NHBPEP . This study thus provides nor-

mative BP percentiles us₁in₃ g currently agreed methods

1

by NHBPEP , the AHA and 1996 update of Task

1

4

Force on Blood Pressure Control in Children for Nige-

rian children age 5 to 15 years. In the absence of BP

standards using currently agreed methods for BP deter-

mination internationally and the non-representation of

African children living in Africa, the normative BP per-

centiles derived in this study would be suitable for use in

Nigerian children. Although there is another Nigerian

study that used at least 40% of cuff width; the study was

on adolescents aged 10 to 18 years and BP percentiles

th

Fig 2: The 5 , 10 , 50 ,

9

th th

0 and 95 percentiles

of the female systolic

blood pressure

6

were not generated .

The prevalence of hypertension in this study is similar to

an earlier Nigerian study on adolescents aged 10 – 18

6

years in Calabar₉b_,₂u₀t lower than some other previous

1

studies in Nigeria . The higher values obtained in the

th

Fig 3: The 5 , 10 , 50 ,

9

previous studies may reflect the differences in the envi-

ronment stressors, weight and parameters affecting BP.

The influence of environment on the casual BP of chil-

th th

0 and 95 percentiles

of the male diastolic

blood pressure

21

dren was demonstrated in a study by Hamidu et al , in

Kaduna State, Nigeria where the place of residence sig-

nificantly influenced the BP of the children from three

3

different communities . The prevalence of hypertension

in this study and most other Nigerian studies is higher

2

than the 1-2% quoted among Caucasian children . This

suggests that the prevalence of childhood hypertension

in Nigeria is higher than that reported amongst Cauca-

sians. It is not clear why this is so. It may be related to

differences in environmental stressors, or genetics.

th

Fig 4: The 5 , 10 , 50 ,

9

th th

0 and 95 percentiles

of the female diastolic

blood pressure

However, childhood essential hypertension is reported

to be on the rise globally and besides the possibility of

inheriting essential hypertension from their affected par-

ents, another important associated factor is obesity and

1

,23

.

overweight whose prevalence is also on the rise

Overweight/ obesity are caused by the sedentary life-

style that includes television watching, video gaming

and less physical exercise. This is further compounded

2

27

2

4

by increased consumption of fast food . Studies have

demonstrated similar lifestyle₉among Nigerian children

who are overweight and obese .

females in this study. Perhaps because females are

encouraged to stay at home and engage in indoor activi-

ties like cooking while the males engage in more physi-

cal activities l_ti_hke playi_tn_h g football and other outdoor

games. The 90 and 95 percentiles for blood pressure

in the males aged ten years and older was lower than

those of the females, this is also due to the fact that the

females were heavier than the males in this study.

It is important to initiate programmes to stop this trend

in Nigeria as this lifestyle among children portends a

potential for higher prevalence of hypertension and other

cardiovascular and metabolic abnormalities if the trend

is not checked. Lessons can be learned from the United

States experience in which a study done in 1994 by Arar

2

5

et al , found that 23% of the hypertensive children had

essential hyp₆ ertension. By 2001 in another study by

Conclusion

2

Flynn et al the proportion of children with essential

hypertension was 48.6%. This rising trend of the burden

of childhood essential hypertension is being attributed to

the rising prevalence of overweight and obesity

In conclusion, BP percentiles were derived for Nigerian

children using cuff sizes based on the arm circumference

in this study. The older females tend to have higher BP

values compared to the males, a reversal of previous

trend involving younger age group. These percentiles

will be appropriate for use in Nigerian children pending

the development of a National BP standard for children

derived using recently agreed cuff specification and

from the different zones of the country and pending

when the BP values of African children resident in Af-

rica are included in a new global BP standard like that of

the NIH. Furthermore, there is a need to initiate a pro-

gramme to address weight reduction in school children,

especially the older girls who are heavier than their male

colleagues.

1

0,11

.

The MSBP and MDBP of the male pupils were lower

than that for the females for most ages; this is at vari-

ance with previous studies that showed a higher BP for

the male compared to the females until adolescence

2

-6

when the females now had higher BP . The lower male

BP in our study may be due to the similarly higher mean

weight for the female than the males for most ages,

showing the pivotal role that weight plays in the predic-

tion of BP as also has been demonstrated by previous

2

-6

studies . The height did not show similar strength of

association also indicating the less important role height

1

plays in prediction of BP . This fact is further but-

tressed by the finding of weight and age as the only in-

dependent predictors of BP in this study.

Conflict of interest: None

Funding: None

It is not clear why the older males were lighter than the

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