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ORIGINAL ARTICLE
Year : 2016  |  Volume : 19  |  Issue : 3  |  Page : 401-406

Blood pressure to height ratio as a screening tool for prehypertension and hypertension in adolescents


1 Department of Paediatrics, College of Medicine, University of Lagos and Lagos University Teaching Hospital, PMB 12003, Idi-Araba, Lagos, Nigeria
2 Department of Pediatrics, Havana Specialist Hospital, 115, Akerele Extension, Surulere, Lagos, Nigeria
3 Department of Paediatrics, College of Health Sciences, University of Port Harcourt, Rivers State, Nigeria

Date of Acceptance03-Dec-2015
Date of Web Publication28-Mar-2016

Correspondence Address:
Dr. T A Ladapo
Department of Paediatrics, College of Medicine, University of Lagos and Lagos University Teaching Hospital, PMB 12003, Idi-Araba, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1119-3077.179289

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   Abstract 

Background: Current methods of detection of childhood hypertension are cumbersome and contribute to under-diagnosis hence, the need to generate simpler diagnostic tools. The blood pressure to height ratio has recently been proposed as a novel screening tool for prehypertension and hypertension in some populations. We evaluated its applicability in our environment.
Materials and Methods: The weights, heights, and blood pressure measurements of 2364 apparently healthy adolescents were determined. Sex-specific systolic and diastolic blood pressure to height ratios (SBPHR) and (DBPHR) were calculated, and their ability to detect prehypertension and hypertension was determined using receiver operating curves. Discriminatory ability was measured by the area under the curve (AUC) and optimal cutoff points along the curve were determined. P < 0.05 was considered statistically significant.
Results: The SBPHR and DBPHR were similar across all age groups and sexes. The AUC of SBPHR and DBPHR for diagnosing prehypertension and hypertension by sex was >0.95 for both diastolic and systolic hypertension in both sexes. It ranged between 0.803 and 0.922 for prehypertension and 0.954–0.978 for hypertension indicating higher accuracy for hypertension. Sensitivity was higher for systolic and diastolic hypertension (90–98%) compared with prehypertension (87–98%). Specificity was lower than sensitivity across all categories of hypertension and prehypertension (0.64–0.88%) though higher for hypertension (0.75–0.88) compared with prehypertension (0.64–0.75).
Conclusion: BPHR is a useful screening tool for prehypertension and hypertension in black adolescents. Accuracy increased with higher degrees of hypertension.

Keywords: Adolescents, blood pressure, height, hypertension


How to cite this article:
Ladapo T A, Fajolu I B, Adeniyi O F, Ekure E N, Maduako R O, Jaja T C, Oduwole A O. Blood pressure to height ratio as a screening tool for prehypertension and hypertension in adolescents. Niger J Clin Pract 2016;19:401-6

How to cite this URL:
Ladapo T A, Fajolu I B, Adeniyi O F, Ekure E N, Maduako R O, Jaja T C, Oduwole A O. Blood pressure to height ratio as a screening tool for prehypertension and hypertension in adolescents. Niger J Clin Pract [serial online] 2016 [cited 2020 Mar 29];19:401-6. Available from: http://www.njcponline.com/text.asp?2016/19/3/401/179289


   Introduction Top


The association of childhood hypertension with cardiovascular morbidity and recognition of its progression to adult hypertension has drawn attention to the need for prompt diagnosis and management in childhood.[1],[2],[3] Pediatric hypertension is diagnosed based on centile charts derived by the United States Task Force on High Blood Pressure in Children and Adolescents.[4] These charts are age, gender, and height centile-dependent and need to be referred to for every child seen. This cumbersome process is often difficult to employ in everyday clinical settings, even for pediatricians and has been proposed to be one of the main factors mitigating blood pressure measurements in children.[5] In a large study in the USA,[5] alarmingly large rates of under-diagnosis of both childhood hypertension and prehypertension were reported. The figures are likely to be higher in developing countries such as ours where health awareness is lower. Clearly, such high rates of undetection could undermine efforts directed at control of hypertension.

In recognition of this challenge, simpler tools for the diagnosis of pediatric high blood pressure have been proposed. The blood pressure height ratio (BPHR) was first proposed as a simple, accurate, and nonage dependent screening index for adolescent hypertension by Lu et al.[6] in China. Subsequently, there have been efforts to validate this tool among Caucasian and Asian populations.[7],[8],[9],[10],[11],[12],[13] Ejike and Ejike,[14],[15] in, to our knowledge, the only reports in blacks, reported similar observations for both prehypertension and hypertension in children from the North Central and South Eastern Regions of Nigeria. One study was in children aged 7–10 years.[14] while the other which was among 1173 adolescents [15] was conducted in a mixture of semiurban and urban areas. Variability in anthropometric indices between geographical regions in Nigeria [16] may, therefore, imply that the findings may not be applicable to all regions of the country. In addition, blood pressure determination was by oscillometric rather than auscultatory methods as recommended by the United States Task Force on High Blood Pressure in Children and Adolescents.[4] The oscillometric method is based on the oscillations of pressure in a sphygmomanometer cuff recorded during gradual deflation, the point of maximal oscillation corresponding to the mean intra-arterial pressure. These oscillations, however, begin well above systolic pressure and continue below diastolic, so that actual pressures can only be estimated indirectly by empirically derived algorithms which vary between manufacturers. This accounts for variations in blood pressure readings between oscillometric in contrast to the mercury sphygmomanometer.[17],[18] The objective of this study, therefore, was to evaluate the BPHR as a screening tool for high blood pressure in a large group of urban dwelling black adolescents using blood pressures derived by auscultation.


   Materials and Methods Top


Study area and population

This cross-sectional, multi-centre study of apparently healthy adolescents aged 10–18 years was conducted in three secondary schools in the South-Western and South-Southern regions of Nigeria. The selection was done via a multi-stage technique. One of the educational districts in each of the states was randomly selected. The secondary schools in one educational zone each from the selected districts were further stratified into single gender and mixed schools. Three mixed gender schools were then selected by simple random methods. Ethical approval was obtained from the Health Research and Ethics Committees of the Lagos University Teaching Hospital, Lagos and the University of Port Harcourt Teaching Hospital, Rivers State, Nigeria. The school authorities gave formal approval while parental written informed consent and student assent were also obtained. Failure to obtain consent led to exclusion from the study. The study conformed to the ethical guidelines and principles of the Helsinki declaration of 2008.

Data collection

All eligible pupils were consecutively enrolled. Details of the nature of the study and its importance were explained to the subjects, and a brief demonstration of the measurement techniques was conducted before the commencement of the study. Data such as age, sex, weight, and height were entered into a study proforma.

Measurements

All measurements were carried out by the researchers and well-trained assistants. A calibrated digital scale was used to obtain the weights of subjects to the nearest 0.1 kg. Each subject was weighed barefoot in light clothing, (belts and other accessories were removed and pockets emptied) and standing still without any support. Height was measured to the nearest 0.5 cm using a stadiometer. Blood pressure was measured using a standard mercury sphygmomanometer and appropriately sized cuffs.[4] Subjects were quietly and comfortably seated with legs uncrossed and feet resting on a firm surface for at least 5 min before measurements were taken.[4] Systolic and diastolic BP readings were recorded at the first and fifth Korotkoff sounds respectively with readings taken to the nearest 2 mmHg during deflation. The average of at least two readings taken with a minimum of 5 min interval was taken as the subject's blood pressure.[4],[19]

Hypertension based on age, sex and height was defined as follows: Prehypertension: - ≥90th–<95th percentile; hypertension ≥95th percentile; Stage 1 hypertension: 95th–99th +5 mmHg; Stage 2 hypertension: >99th percentile +5 mmHg.[4],[20] Blood pressure >120/80 mmHg but <90th centile was also defined as prehypertension. For adolescents aged 18 years, blood pressure <120/80 mmHg was considered normal and hypertension was defined as follows:[21] Prehypertension: 120–139/80–89 mmHg; Stage 1 hypertension: 140–159/90–99 mmHg; Stage 2 hypertension: >160/100 mmHg. Systolic blood pressure to height ratio (SBPHR) and diastolic blood pressure to height ratio (DBPHR) were calculated as follows: SBP (mmHg)/height (cm) and DBP (mmHg)/height (cm), respectively.

Statistical analysis

Data were analyzed using the Statistical Package for Social Sciences version 20. (SPSS Inc., Chicago, IL, USA). Continuous data were represented as means and standard deviation while categorical data were represented as percentages. Statistical significance for discrete data was determined using the Chi-square test while comparison of means was done using the Student's t-test. Receiver operating curves (ROC) were generated to test the ability of the SBPHR and DBPHR to detect prehypertension and hypertension in males and females independently. The discriminatory ability was measured by the area under the curve (AUC) and classified as follows: 0.9 to < 1: Excellent, 0.8 t < 0.9: Good, 0.7 < 0.8: Worthless, and 0.6–< 0.7: Not good.[22] The ROC is a plot of sensitivity against 1-specificity for a range of cut-off points of SBPHR and DBPHR to the SBP and DBP. The optimal cut-off points were taken as the points where maximal sensitivity and specificity were achieved along the curve. P < 0.05 was considered statistically significant.


   Results Top


A total of 2364 adolescents (M: F: 0.69:1), whose ages ranged from 10 to 18 years with mean age of 14.1 ± 2.1 years were studied. Subjects were divided into three age-groups for the purpose of analyzing descriptive characteristics as follows: (10–12 years, 13–15 years and 16–18 years) [Table 1]. Majority (46.6%) were aged between 13 and 15 years with the rest being almost equally split between the other age-groups. The mean weight, height, SBP and DBP increased with age in both sexes. The SBPHR and DBPHR, however, did not observe this trend being similar across all age groups and sexes, ranging between 0.69–0.72 and 0.42–0.45 respectively. Both SBPHR and DBPHR were generally higher in females across all age groups.
Table 1: Descriptive characteristics of 2364 study participants by age and gender

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Comparison of overall mean variables between both sexes in [Table 2] showed a trend to higher values in females for weight while mean height demonstrated a trend to higher values in males, although only the height difference was statistically significant. Overall prevalence rates of systolic and diastolic hypertension were 5.3% and 4%, respectively with corresponding prehypertension prevalence rates of 16.6% and 7.7%, respectively [Table 3]. Prevalence of systolic hypertension was higher in males while that of diastolic hypertension was higher in females though the differences did not reach statistical significance.
Table 2: Comparison of means of variables in 2364 study subjects between sexes

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Table 3: Pattern of hypertension in study subjects

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The AUC statistics of SBPHR and DBPHR for diagnosing prehypertension and hypertension by sex are shown in [Table 4] and [Figure 1] and [Figure 2]. The value was >0.95 for both diastolic and systolic hypertension in both sexes and ranged between 0.803 and 0.922 for prehypertension indicating greater accuracy for hypertension. Optimal cut-off points and corresponding sensitivities and specificities are shown in [Table 5]. Sensitivities for both systolic and diastolic hypertension ranged from 90% to 98% while that for prehypertension ranged from 87% to 98%. Sensitivities were also higher in females for all categories of hypertension. Specificity was lower than sensitivity across all categories of hypertension and prehypertension ranging from 0.64% to 0.88% but was higher for hypertension (0.75–0.88) compared with prehypertension (0.64–0.75).
Figure 1: Receiver operating curves for systolic blood pressure to height ratio (a and b) and diastolic blood pressure to height ratio (c and d) for discrimination between children with and those without prehypertension by gender

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Figure 2: Receiver operating curves for systolic blood pressure to height ratio (a and b) and diastolic blood pressure to height ratio (c and d) for discrimination between children with and those without hypertension by gender

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Table 4: Gender-specific area under the curve of SBP and DBP to height ratios

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Table 5: Optimal thresholds of SBP and DBP to height ratios for diagnosing prehypertension and hypertension and their corresponding sensitivities and specificities

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   Discussion Top


Childhood hypertension has reached epidemic proportions worldwide, largely associated with the rising prevalence of childhood obesity.[23],[24],[25],[26],[27] The prevalences of systolic and diastolic hypertension in the present study were 5.3% and 4%, respectively while those of systolic and diastolic preprehypertension were 16.7% and 7.7%, respectively supporting this trend. In another developing country, overall prevalences of 3.4% and 10.6% were reported for hypertension and prehypertension, respectively.[27] This supports the recent global attention on the need for routine blood pressure measurement in childhood to enable prompt diagnosis and intervention. The BPHR is a recently identified screening tool for childhood hypertension and prehypertension. It is proposed that this tool will significantly improve hypertension detection rates by simplifying diagnosis, in contrast to the current cumbersome process that requires referral to age and sex-specific charts for each child seen.[4]

In the current study, the SBPHR and DBPHR were similar across all age groups and sexes despite variations of blood pressure, weight, and height with age suggesting that the ratio should perform well across the adolescent age-group. It also implies that the performance of the tool may be unaffected by differences in these variables that may exist between different populations. This is an important characteristic that should promote its recommendation as an internationally accepted tool for blood pressure screening in children. The AUC for SBPHR and DBPHR in both sexes demonstrated excellent ability to predict blood pressure status. The predictive ability was however higher for hypertension being >0.90 in all categories compared to prehypertension which ranged from 0.803 to 0.922. This is similar to the findings of other workers from China and Nigeria [7],[13],[14] who reported AUC values that increased with the degree of hypertension in both young children aged 5–12 years old and adolescents. Galescu et al.[10] from the USA, however, reported higher AUC values of >0.95 for both SBP and DBP. In that study, there was no differentiation between prehypertension and hypertension as all children with blood pressure >90th centile for age and sex were analyzed as a group which could have accounted for their findings. In summary, BPHR as a screening tool for elevated blood pressure in children appears to perform better for hypertension than prehypertension. Repeated blood pressure measurements in childhood may, however, help circumvent this limitation as pre-hypertensive children who are initially missed may be diagnosed during future blood pressure measurements. This highlights the importance of the recommendation of the American National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents,[4] that all children above the age of 3 years admitted to a health facility should have their blood pressures checked.

The optimal thresholds of SBPHR and DBPHR for diagnosis of prehypertension and hypertension were similar to those from most previous studies. These range from 0.70 to 0.73 for systolic prehypertension, 0.75–0.79 for systolic hypertension, 0.45–0.48 for diastolic prehypertension and 0.48–0.51 for diastolic hypertension.[6],[7],[8],[9],[10],[12],[13],[14],[15],[23] These striking similarities between studies in various populations is encouraging and again presupposes the general applicability of this novel screening tool.

Sensitivities and specificities derived from our study were generally higher for hypertension in comparison with prehypertension which aligns with most other reports, re-affirming the better performance of the test for hypertension versus prehypertension. In addition, the test demonstrated higher sensitivity than specificity across all ranges of blood pressures in all sexes in our study subjects. This was similar for most reported studies [6],[7],[10],[14],[15] except for that by Keliashi [9] from the Middle East where this pattern was only observed for predominantly prehypertension in both sexes. This is significant as with this type of screening tool; it is more desirable to have a higher rate of false positives (higher sensitivity) who can be subsequently excluded by further blood pressure measurements than false negatives (higher specificity) in which case hypertensive children may escape diagnosis.

The performance of the ratio is largely independent of race as has been reported.[7], 8, [10],[11],[12],[13],[14] This, in addition to promising studies in younger children [7],[11],[12],[13],[14] again demonstrates the potential for wide applicability of the BPHR as a screening tool for childhood hypertension. In the current study, blood pressure was derived from the average of two measurements obtained at a single visit similar to the study by Outdili et al.[12] This aligns with their claim that the use of this tool does not require repeated visits which is another potential advantage for its use. It should, however, be emphasized that it is only a screening tool, hence standard reference charts [4] should still be referred to confirmation of diagnosis.[4]

Totaro et al.[23] compared the BPHR with other previously described blood pressure screening tools (Somu's equations, Ardissino's table, and Kaelber's table) and found BPHR to be the best compromise between sensitivity (an important feature of a screening test) and accuracy. The authors concluded that that the BPHR is an easy-to-apply test that allows the identification of hypertensive children with only four thresholds and can, therefore, be used in any setting. The findings of the present study lend credence to this observation.


   Conclusion Top


This study adds to the increasing body of evidence that the BPHR performs well as a simple screening tool for prehypertension and hypertension in adolescents of all races. Larger studies in younger children and other populations as well as systematic reviews are recommended.

Acknowledgments

The authors are grateful to the research assistants who helped to obtain the measurements from the study participants and the staff of the participating schools.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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