Original article
Blood pressure to height ratio: A novel method for detecting hypertension in paediatric age groups Xiaofan Guo MD1, Liqiang Zheng MD2, Yang Li MD1, Xingang Zhang MD1, Shasha Yu MD1, Yingxian Sun MD PhD1 X Guo, L Zheng, Y Li, X Zhang, s Yu, Y sun. Blood pressure to height ratio: A novel method for detecting hypertension in paediatric age groups. Paediatr Child health 2013;18(2):65-69.
Le ratio entre la tension artérielle et la taille : une nouvelle méthode pour déceler l’hypertension dans les groupes d’âge pédiatrique
BACkGround: A novel method for detecting hypertension in paediatric age groups has recently been formulated using ratios of systolic blood pressure to height (SBPHR) and diastolic blood pressure to height (DBPHR). AiM: To validate this approach and assess its applicability to children. Methods: A cross-sectional study of 6837 children and adolescents five to 18 years of age was conducted. Blood pressure (BP) readings obtained were stratified using population-based percentiles from the United States. resuLts: For SBPHR and DBPHR, areas under the ROC curve were >0.9 for BP at or above the 95th percentile. Performance of the cut-off points for detecting elevated BP in adolescents 13 to 18 years of age compared favourably with previous studies, showing high sensitivity and specificity (>95%). SBPHR and DBPHR also proved satisfactory when applied to children five to 12 years of age. Nevertheless, performance was lower for BP between the 90th and 95th percentiles. ConCLusions: BP to height ratios are a practical means for detecting elevated BP in adolescents and children.
historiQue : Une nouvelle méthode pour dépister l’hypertension dans les groupes d’âge pédiatrique a récemment été formulée au moyen du ratio entre la tension artérielle systolique et la taille (RTAST) et du ratio entre la tension artérielle diastolique et la taille (RTADT). oBJeCtiF : Valider cette méthode et en évaluer l’applicabilité chez les enfants. MÉthodoLoGie : Les chercheurs ont procédé à une étude transversale auprès de 6 837 enfants et adolescents de cinq à 18 ans. Ils ont stratifié les lectures de tension artérielle (TA) obtenues au moyen de percentiles en population provenant des États-Unis. rÉsuLtAts : Pour ce qui est du RTAST et du RTADT, les aires sous la courbe ROC étaient supérieures à 0,9 lorsque la TA se situait au moins au 95e percentile. Le rendement des seuils pour déceler une TA élevée chez les adolescents de 13 à 18 ans se comparait favorablement à celui d’études antérieures, démontrant une sensibilité et une spécificité élevées (supérieures à 95 %). Le RTAST et le RTADT se sont également révélés satisfaisants lorsqu’on les appliquait aux enfants de cinq à 12 ans, mais le rendement était moins élevé lorsque la TA se situait entre le 90e et le 95e percentile. ConCLusions : Les ratios entre la TA et la taille représentent un moyen pratique de dépister une TA élevée chez les adolescents et les enfants.
key Words: Adolescents; Blood pressure to height ratio; Children; Hypertension; Prehypertension
H
ypertension/high blood pressure (HBP) is an emerging health issue of considerable importance in children and adolescents due to its rising prevalence in many areas and associated consequences. Although the worldwide prevalence in youths is not precisely known, high rates reported for various age groups, regions and races all indicate a global problem (1-6). There is increasing evidence that elevated BP in childhood is associated with target organ damage, notably left ventricular hypertrophy, which may result in premature cardiovascular morbidity and mortality in adults (7-9), and commonly leads to hypertension in young adulthood (10). Because HBP in childhood is often asymptomatic and, thus, is easily overlooked (even by health professionals), almost 75% of cases (90% with prehypertension) reportedly go undiagnosed (11). However, given the complexity of defining paediatric-onset HBP (via sex, age and height percentiles), the technical issues involved (such as appropriate cuff size) and the paucity of available diagnostic guidance, it is understandable why current detection rates are low. Although a simplified table developed by Kaelber et al (12) has enabled quick and easy identification of children and adolescents whose BP readings need further evaluation, it still requires consulting many normative values, which may not be readily available.
Recently, Lu et al (13) developed novel criteria, using ratios of systolic BP to height (SBPHR) and diastolic BP to height (DBPHR) to identify HBP in Chinese Han adolescents. Diagnostic sensitivity and specificity were excellent with this method. Another study involving Caucasian adolescents (14) has subsequently substantiated the initial success, but the epidemiological merit of this technique has yet to be proven in children. Therefore, we chose to evaluate this approach with the following objectives in mind: to validate previous results via a sampling of adolescents from northern China; to determine applicability to children (five to 12 years of age); to determine optimal ratio cut-off points; and to investigate its utility in paediatric prehypertensive states.
Methods
From July 2010 to January 2011, a cross-sectional study in rural Shenyang, Liaoning Province (China) was conducted using a BP to height ratio (BPHR) to detect prehypertension and hypertension in Chinese children and adolescents. A total of 7673 students five to 18 years of age were recruited from 12 public schools by multistage cluster sampling (socioeconomic class discounted). The exclusion criteria were major medical conditions, such as chronic heart, renal or hepatic disease, infections, trauma within two weeks and medication use. Informed consent was obtained from the
1Department
of Cardiology, the First Hospital of China Medical University; 2Department of Clinical Epidemiology, Library, Shengjing Hospital of China Medical University, Shenyang, People’s Republic of China Correspondence: Dr Yingxian Sun, Department of Cardiology, the First Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang 110001, People’s Republic of China. Telephone 86-24-83282688; fax 86-24-83282346; e-mail [email protected] Accepted for publication November 22, 2012
Paediatr Child Health Vol 18 No 2 February 2013
©2013 Pulsus Group Inc. All rights reserved
65
Guo et al
Table 1 baseline characteristics of subjects according to sex and age Total (n=6837)
boys (n=3640)
Girls (n=3197)
9.4±1.8
9.3±1.8 31.0 (26.0–38.0)
Five to 12 years of age (n=4583) Age, years, mean ± SD
9.4±1.8
Weight, kg
32.0 (27.0–39.0)
32.0 (28.0–40.0)
Height, cm
136.0 (127.5–144.2)
136.0 (128.0–144.0) 135.5 (127.0–144.6)
BMI, kg/m2
17.1 (15.8–19.2)
17.5 (16.1–19.9)
16.8 (15.6–18.6)
SBP, mmHg
104.5 (96.0–112.5)
105.0 (98.0–113.0)
102.5 (95.0–112.0)
DBP, mmHg
65.0 (59.0–71.0)
65.0 (60.0–72.0)
64.0 (58.0–71.0)
SBPHR, mmHg/cm, mean ± SD
0.77±0.09
0.78±0.09
0.77±0.09
DBPHR, mmHg/cm, mean ± SD
0.48±0.07
0.48±0.07
0.48±0.07
14.1±1.0
14.0±1.0
13 to 18 years of age (n=2254) Age, years, mean ± SD
14.1±1.0
Weight, kg
50.5 (44.5–58.5)
52.1 (45.1–62.9)
48.5 (44.0–54.6)
Height, cm
159.0 (154.0–164.5)
162.2 (156.0–167.6)
157.0 (153.0–160.5)
19.7 (18.0–22.4)
19.8 (18.0–23.0)
BMI, kg/m2 SBP, mmHg
116.5 (108.0–125.0) 117.5 (108.0–125.0)
19.7 (18.0–22.0) 115.0 (107.5–122.5)
DBP, mmHg
70.0 (65.0–77.5)
70.0 (63.0–77.5)
70.3 (67.5–79.0)
SBPHR, mmHg/cm, mean ± SD
0.73±0.08
0.73±0.07
0.74±0.08
DBPHR, mmHg/cm, mean ± SD
0.45±0.06
0.43±0.06
0.46±0.06
Data are presented as 50th (25th to 75th) percentiles unless otherwise indicated. BMI Body mass index; DBP Diastolic blood pressure; DBPHR Diastolic blood pressure to height ratio; SBP Systolic blood pressure; SBPHR Systolic blood pressure to height ratio
parents or guardians of all subjects. The final sample consisted of 6837 students (3640 boys, 3197 girls), with an overall response rate of 89.1%. The present study was approved by the Ethics Committee of China Medical University (Shenyang, China). According to the standardized technique described by the American Heart Association (15), BP was measured by welltrained personnel from the bare right arm of participants, at the level of the heart, while participants remained seated with back support, after at least 5 min of rest. A calibrated mercury sphygmomanometer with appropriate cuff length was used. Participants were advised to avoid coffee, tea, stimulant foods, smoking and exercise for at least 30 min before the measurements. Two measurements were taken and averaged for analysis. All BP data were subsequently stratified using United States population-based percentiles (15). Normal BP was defined as an average systolic BP (SBP) and/or diastolic BP (DBP) 80 mmHg for adolescents. HBP (stages 1 and 2) was defined as average SBP and/or DBP ≥95th percentile, while average SBP and/or DBP >99th percentile plus 5 mmHg indicated stage 2 disease. Anthropometric data for all subjects, including height and body weight, were evaluated by specialists (cardiologists, internists and paediatricians) using standard protocols. Using a portable 66
stadiometer, the height of each subject (light clothing, no shoes) was measured to the nearest 0.5 cm. Body weight to the nearest 100 g was measured using a professional scale, and the body mass index was calculated (weight [kg]/height2 [m2]). SBPHR was calculated as SBP (mmHg)/height (cm) and DBPHR as DBP (mmHg)/height (cm). Data are expressed as mean ± SD or percentiles. Pearson’s or Spearman’s correlation coefficients were used to identify interrelating variables. Height was controlled when the relationships between age and BPHR were analyzed using partial correlation analysis. To test the value of the ratios (SBPHR and DBPHR) in detecting prehypertension and HBP (stages 1 and 2), ROC analysis was used. ROC curves plot sensitivity (true-positive ratio) by one minus the specificity (true-negative ratio) for a series of cut-off points established by SBPHR and DBPHR to the age-, sex- and height-specific SBP and DBP references, respectively. The area under the ROC curve (AUC) represents an overall measurement of performance of the test, with 1.0 representing a perfect test and 0.5 a test with no discriminating capacity. A test with an AUC of ≥0.85 was considered to be an accurate test (16). The optimal cut-off points were determined on the basis of ROC curve analysis where the sum of sensitivity and specificity achieved maximum, and prehypertension and HBP were defined using optimal cut-off points of SBPHR and DBPHR. Corresponding levels of sensitivity and specificity were then calculated. All data were analyzed using SPSS version 17.0 (IBM Corporation, USA), with statistical significance set at P99th + 5 mmHg
0.99 (0.97–0.996)
0.99 (0.99–1.00)
SBP ≥95th
0.94 (0.93–0.95)
0.98 (0.97–0.98)
DBP ≥95th
0.96 (0.95–0.97)
0.98 (0.98–0.99)
Table 5 Sensitivity and specificity of systolic blood pressure to height ratio and diastolic blood pressure to height ratio for diagnosis of high blood pressure in children and adolescents
All P90th and 99th + 5 mmHg
Thresholds, 0.81/0.50 0.77/0.50 0.84/0.54 0.83/0.53 0.87/0.63 0.87/0.59 mmHg/cm Sensitivity
0.87
0.94
0.92
0.91
0.98
0.94
Specificity
0.57
0.55
0.81
0.81
0.87
0.86
13 to 18 years of age (n=2254) Thresholds, 0.71/0.46 0.73/0.48 0.77/0.48 0.79/0.51 0.84/0.55 0.85/0.57 mmHg/cm
boys
Girls
boys
Girls
boys
Girls
Sensitivity
0.90
0.97
0.96
0.93
0.97
0.97
Cut-off points
0.81
0.77
0.84
0.83
0.87
0.87
Specificity
0.47
0.52
0.87
0.91
0.96
0.96
Sensitivity
0.76
0.91
0.90
0.87
1.00
0.93
Specificity
0.79
0.71
0.86
0.86
0.87
0.89
DbP >90th and 99th + 5 mmHg boys
Girls
Cut-off points
0.50
0.50
0.54
0.53
0.63
0.59
Sensitivity
0.96
0.94
0.97
0.92
1.00
1.00
Specificity
0.77
0.79
0.88
0.86
0.98
0.94
90th 90th percentile; 95th 95th percentile; 99th 99th percentile; DBP Diastolic blood pressure; SBP Systolic blood pressure
Table 3 presents the optimal cut-off points of SBPHR and DBPHR for identifying elevated SBP and DBP among children. The optimal thresholds for identifying SBP >99th percentile plus 5 mmHg were both 0.87 for boys and girls, while those for DBP >99th percentile plus 5 mmHg were 0.63 in boys and 0.59 in girls. The optimal thresholds for identifying SBP ≥95th percentile were 0.84 in boys and 0.83 in girls, while that for DBP ≥95th percentile were 0.54 in boys and 0.53 in girls. Sensitivities and specificities were lower for the identification of the level of SBP and DBP >90th and ≤95th percentiles. Table 4 presents the optimal cut-off points of SBPHR and DBPHR as well as corresponding sensitivity and specificity among adolescents. The optimal thresholds for detecting elevated BP at all levels were lower than those found among Paediatr Child Health Vol 18 No 2 February 2013
children. However, sensitivity and specificity in this age group were much higher. Table 5 presents the sensitivity and specificity of SBPHR and DBPHR for the identification of HBP status in both children and adolescents. The detection value in stage 2 HBP was found to be highest. Among adolescents, the sensitivities for detecting stage 2 HBP were both 97% in boys and girls, and the specificities were both 96% in boys and girls. The detection value in children was lower than that in adolescents, with sensitivities of 98% in boys and 94% in girls, and specificities of 87% in boys and 86% in girls for identifying stage 2 HBP.
disCussion
In the present cross-sectional study of 6837 children and adolescents, we found a relatively high overall prevalence of HBP (20.4%) and prehypertension (14.9%). The AUCs of SBPHR and DBPHR for detecting different levels of elevated BP were all >0.9 except for the range from the 90th to 95th percentile in both sexes across all ages. Among adolescents, SBPHR and DBPHR were good diagnostic markers for HBP, especially for stage 2 (sensitivities and specificities were >95% in both sexes). Although the specificities of BPHR for identifying HBP were not as high as sensitivities in children, the diagnostic efficiency remained acceptable. 67
Guo et al
As a consequence of epidemic paediatric obesity, paediatriconset HBP is on the rise in many areas. A dramatically increasing rate of HBP among children and adolescents was reported in the China Health and Nutrition Surveys, with an increase of prevalence from 7.1% in 1991 to 14.6% in 2004 (3). National Health and Nutrition Examination Surveys (NHANES) also indicated an increasing trend of BP in this segment of the population, showing that mean SBP and DBP increased by 1.4 mmHg and 3.3 mmHg, respectively, between the time periods from 1988 to 1994, and 1999 to 2000 (17). Consistent with our previous studies on adults, we observed a relatively high prevalence of hypertension in rural areas of northern China among children and adolescents. Based on the publication by Hansen et al (11), the underdiagnosis of HBP among children and adolescents has increasingly drawn attention. Many reasons related to the measurement and interpretation of BP may account for this high rate, to which the complicated and cumbersome diagnostic criteria contributed the most. Although using sex-, age- and height-specific percentiles to define childhood hypertension could achieve more precision and avoid overdiagnosis, its inconvenience and complexity limited its application in self-assessment and monitoring. To reduce future cardiovascular impact through early intervention, developing a practical, simple and highly accurate detection method is an urgenct necessity. In growing children and adolescents, height and age are highly correlated. Many studies have shown that both age and height are important determinants of HBP in young age groups (18-20). Height is also independently related to BP independent of age (21,22), highlighting the importance of height in defining paediatric hypertension. Therefore, it is reasonable to base this detection method on the use of BPHR, which showed strong correlation with SBP and DBP and weak correlation with age. Advantages of this particular method were addressed in greater detail by Lu et al (13). The present work compares favourably with the study by Lu et al (13), which was restricted to adolescents. Ratio (SBPHR and DBPHR) cut-off points for HBP in adolescents were similar, although the sensitivities and specificities we recorded were not quite as high. The outcomes were sufficient to validate this method, especially for identifying stage 2 HBP. We, therefore, advocate BPHR as an effective means of detecting HBP in adolescents. However, in this age group, we found that the specificities of BPHR for identifying prehypertension were relatively low in spite of acceptable sensitivities. To our knowledge, the present study was the first to examine BPHR values for the detection of HBP in children five to 12 years of age. All AUCs were >0.9 (except that of SBPHR for the level of the 90th to 95th percentiles) indicating good discriminating capacities. In identifying stage 2 HBP, the sensitivities were approximately 98% for boys and 94% for girls, and the specificities were approximately 87% for boys and 86% for girls. The AUC results for children, especially the specificities, were not as high as those observed among adolescents; however, we still suggest that this method may offer new detection criteria for childhood HBP, particularly for stage 2 HBP. It is possible to miss prehypertension using this method due to the low specificities in both sexes. Considering that the endocrine status and psychosocial states are dramatically different between the two sexes, we chose to perform sex-specific analyses. To be more precise and to facilitate comparison with previous studies (13,14), we also provided cut-off points for each sex. The strength of the present study was that we first examined this method among children based on a representative population 68
using a relatively large sample size. However, there are some limitations to the present study. First, participants in the study were not sufficiently ethnically diverse to facilitate extrapolation to all ethnic groups. Given the large differences in BP across ethnic groups (23), these new criteria need to be tested further in other ethnicities. Second, because the BP measurements were based on only one visit, the prevalence of HBP may be overestimated in the present study. BP tends to decrease in subsequent visits and HBP should be based on measurements taken over several visits (15). If possible, BP should be measured on multiple visits at different times.
ConCLusion
The ROC analysis in the present study confirmed satisfactory performance of BPHR for detection of HBP in children and adolescents, especially at stage 2. This novel method reduces hundreds of detection values to eight for each age group, with relatively high sensitivities and specificities. Therefore, we advocate the use of BPHR as a simple and practical means of detecting overt HBP (but not prehypertension) in these paediatric age groups.
reFerenCes
1. Ejike CE, Ugwu CE, Ezeanyika LU. Variations in the prevalence of point (pre)hypertension in a Nigerian school-going adolescent population living in a semi-urban and an urban area. BMC Pediatr 2010;10:13. 2. Rafraf M, Gargari BP, Safaiyan A. Prevalence of prehypertension and hypertension among adolescent high school girls in Tabriz, Iran. Food Nutr Bull 2010;31:461-5. 3. Liang YJ, Xi B, Hu YH, et al. Trends in blood pressure and hypertension among Chinese children and adolescents: China Health and Nutrition Surveys 1991–2004. Blood Press 2010;20:45-53. 4. Sharma A, Grover N, Kaushik S, Bhardwaj R, Sankhyan N. Prevalence of hypertension among school children in Shimla. Indian Pediatr 2010;47:873-6. 5. Rosa ML, Fonseca VM, Oigman G, Mesquita ET. Arterial prehypertension and elevated pulse pressure in adolescents: Prevalence and associated factors. Arq Bras Cardiol 2006;87:46-53. 6. Moore WE, Eichner JE, Cohn EM, Thompson DM, Kobza CE, Abbott KE. Blood pressure screening of school children in a multiracial school district: The Healthy Kids Project. Am J Hypertens 2009;22:351-6. 7. Lande MB, Carson NL, Roy J, Meagher CC. Effects of childhood primary hypertension on carotid intima media thickness: A matched controlled study. Hypertension 2006;48:40-4. 8. Drukteinis JS, Roman MJ, Fabsitz RR, et al. Cardiac and systemic hemodynamic characteristics of hypertension and prehypertension in adolescents and young adults: The Strong Heart Study. Circulation 2007;115:221-7. 9. McNiece KL, Gupta-Malhotra M, Samuels J, et al. Left ventricular hypertrophy in hypertensive adolescents: Analysis of risk by 2004 National High Blood Pressure Education Program Working Group staging criteria. Hypertension 2007;50:392-5. 10. Tirosh A, Afek A, Rudich A, et al. Progression of normotensive adolescents to hypertensive adults: A study of 26,980 teenagers. Hypertension 2010;56:203-9. 11. Hansen ML, Gunn PW, Kaelber DC. Underdiagnosis of hypertension in children and adolescents. JAMA 2007;298:874-9. 12. Kaelber DC, Pickett F. Simple table to identify children and adolescents needing further evaluation of blood pressure. Pediatrics 2009;123:e972-4. 13. Lu Q, Ma CM, Yin FZ, Liu BW, Lou DH, Liu XL. How to simplify the diagnostic criteria of hypertension in adolescents. J Hum Hypertens 2011;25:159-63. 14. Rabbia F, Rabbone I, Totaro S, et al. Evaluation of blood pressure/ height ratio as an index to simplify diagnostic criteria of hypertension in Caucasian adolescents. J Hum Hypertens 2011;25:623-4. 15. National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents: The fourth
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bPHR: a novel method for detecting hypertension
16. 17. 18. 19.
report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. Pediatrics 2004;114:555-76. Zou KH, O’Malley AJ, Mauri L. Receiver-operating characteristic analysis for evaluating diagnostic tests and predictive models. Circulation 2007;115:654-7. Muntner P, He J, Cutler JA, Wildman RP, Whelton PK. Trends in blood pressure among children and adolescents. JAMA 2004;291:2107-13. Rosner B, Cook N, Portman R, Daniels S, Falkner B. Determination of blood pressure percentiles in normal-weight children: Some methodological issues. Am J Epidemiol 2008;167:653-66. Rosner B, Prineas RJ, Loggie JM, Daniels SR. Blood pressure nomograms for children and adolescents, by height, sex, and age, in the United States. J Pediatr 1993;123:871-86.
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20. Chadha SL, Vasan RS, Sarma PS, Shekhawat S, Tandon R, Gopinath N. Age- and height-specific reference limits of blood pressure of Indian children. Natl Med J India 1999;12:150-6. 21. Gillum RF, Prineas RJ, Horibe H. Maturation vs age: Assessing blood pressure by height. J Natl Med Assoc 1982;74:43-6. 22. Wang Z, Ma J, Dong B, Song Y, Hu PJ, Zhang B. Comparison of blood pressure levels among four age groups of Chinese children matched by height. J Hum Hypertens 2012;26:437-42. 23. Rosner B, Cook N, Portman R, Daniels S, Falkner B. Blood pressure differences by ethnic group among United States children and adolescents. Hypertension 2009;54:502-8.
69
Blood pressure to height ratio: A novel method for detecting hypertension in paediatric age groups Xiaofan Guo MD1, Liqiang Zheng MD2, Yang Li MD1, Xingang Zhang MD1, Shasha Yu MD1, Yingxian Sun MD PhD1 X Guo, L Zheng, Y Li, X Zhang, s Yu, Y sun. Blood pressure to height ratio: A novel method for detecting hypertension in paediatric age groups. Paediatr Child health 2013;18(2):65-69.
Le ratio entre la tension artérielle et la taille : une nouvelle méthode pour déceler l’hypertension dans les groupes d’âge pédiatrique
BACkGround: A novel method for detecting hypertension in paediatric age groups has recently been formulated using ratios of systolic blood pressure to height (SBPHR) and diastolic blood pressure to height (DBPHR). AiM: To validate this approach and assess its applicability to children. Methods: A cross-sectional study of 6837 children and adolescents five to 18 years of age was conducted. Blood pressure (BP) readings obtained were stratified using population-based percentiles from the United States. resuLts: For SBPHR and DBPHR, areas under the ROC curve were >0.9 for BP at or above the 95th percentile. Performance of the cut-off points for detecting elevated BP in adolescents 13 to 18 years of age compared favourably with previous studies, showing high sensitivity and specificity (>95%). SBPHR and DBPHR also proved satisfactory when applied to children five to 12 years of age. Nevertheless, performance was lower for BP between the 90th and 95th percentiles. ConCLusions: BP to height ratios are a practical means for detecting elevated BP in adolescents and children.
historiQue : Une nouvelle méthode pour dépister l’hypertension dans les groupes d’âge pédiatrique a récemment été formulée au moyen du ratio entre la tension artérielle systolique et la taille (RTAST) et du ratio entre la tension artérielle diastolique et la taille (RTADT). oBJeCtiF : Valider cette méthode et en évaluer l’applicabilité chez les enfants. MÉthodoLoGie : Les chercheurs ont procédé à une étude transversale auprès de 6 837 enfants et adolescents de cinq à 18 ans. Ils ont stratifié les lectures de tension artérielle (TA) obtenues au moyen de percentiles en population provenant des États-Unis. rÉsuLtAts : Pour ce qui est du RTAST et du RTADT, les aires sous la courbe ROC étaient supérieures à 0,9 lorsque la TA se situait au moins au 95e percentile. Le rendement des seuils pour déceler une TA élevée chez les adolescents de 13 à 18 ans se comparait favorablement à celui d’études antérieures, démontrant une sensibilité et une spécificité élevées (supérieures à 95 %). Le RTAST et le RTADT se sont également révélés satisfaisants lorsqu’on les appliquait aux enfants de cinq à 12 ans, mais le rendement était moins élevé lorsque la TA se situait entre le 90e et le 95e percentile. ConCLusions : Les ratios entre la TA et la taille représentent un moyen pratique de dépister une TA élevée chez les adolescents et les enfants.
key Words: Adolescents; Blood pressure to height ratio; Children; Hypertension; Prehypertension
H
ypertension/high blood pressure (HBP) is an emerging health issue of considerable importance in children and adolescents due to its rising prevalence in many areas and associated consequences. Although the worldwide prevalence in youths is not precisely known, high rates reported for various age groups, regions and races all indicate a global problem (1-6). There is increasing evidence that elevated BP in childhood is associated with target organ damage, notably left ventricular hypertrophy, which may result in premature cardiovascular morbidity and mortality in adults (7-9), and commonly leads to hypertension in young adulthood (10). Because HBP in childhood is often asymptomatic and, thus, is easily overlooked (even by health professionals), almost 75% of cases (90% with prehypertension) reportedly go undiagnosed (11). However, given the complexity of defining paediatric-onset HBP (via sex, age and height percentiles), the technical issues involved (such as appropriate cuff size) and the paucity of available diagnostic guidance, it is understandable why current detection rates are low. Although a simplified table developed by Kaelber et al (12) has enabled quick and easy identification of children and adolescents whose BP readings need further evaluation, it still requires consulting many normative values, which may not be readily available.
Recently, Lu et al (13) developed novel criteria, using ratios of systolic BP to height (SBPHR) and diastolic BP to height (DBPHR) to identify HBP in Chinese Han adolescents. Diagnostic sensitivity and specificity were excellent with this method. Another study involving Caucasian adolescents (14) has subsequently substantiated the initial success, but the epidemiological merit of this technique has yet to be proven in children. Therefore, we chose to evaluate this approach with the following objectives in mind: to validate previous results via a sampling of adolescents from northern China; to determine applicability to children (five to 12 years of age); to determine optimal ratio cut-off points; and to investigate its utility in paediatric prehypertensive states.
Methods
From July 2010 to January 2011, a cross-sectional study in rural Shenyang, Liaoning Province (China) was conducted using a BP to height ratio (BPHR) to detect prehypertension and hypertension in Chinese children and adolescents. A total of 7673 students five to 18 years of age were recruited from 12 public schools by multistage cluster sampling (socioeconomic class discounted). The exclusion criteria were major medical conditions, such as chronic heart, renal or hepatic disease, infections, trauma within two weeks and medication use. Informed consent was obtained from the
1Department
of Cardiology, the First Hospital of China Medical University; 2Department of Clinical Epidemiology, Library, Shengjing Hospital of China Medical University, Shenyang, People’s Republic of China Correspondence: Dr Yingxian Sun, Department of Cardiology, the First Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang 110001, People’s Republic of China. Telephone 86-24-83282688; fax 86-24-83282346; e-mail [email protected] Accepted for publication November 22, 2012
Paediatr Child Health Vol 18 No 2 February 2013
©2013 Pulsus Group Inc. All rights reserved
65
Guo et al
Table 1 baseline characteristics of subjects according to sex and age Total (n=6837)
boys (n=3640)
Girls (n=3197)
9.4±1.8
9.3±1.8 31.0 (26.0–38.0)
Five to 12 years of age (n=4583) Age, years, mean ± SD
9.4±1.8
Weight, kg
32.0 (27.0–39.0)
32.0 (28.0–40.0)
Height, cm
136.0 (127.5–144.2)
136.0 (128.0–144.0) 135.5 (127.0–144.6)
BMI, kg/m2
17.1 (15.8–19.2)
17.5 (16.1–19.9)
16.8 (15.6–18.6)
SBP, mmHg
104.5 (96.0–112.5)
105.0 (98.0–113.0)
102.5 (95.0–112.0)
DBP, mmHg
65.0 (59.0–71.0)
65.0 (60.0–72.0)
64.0 (58.0–71.0)
SBPHR, mmHg/cm, mean ± SD
0.77±0.09
0.78±0.09
0.77±0.09
DBPHR, mmHg/cm, mean ± SD
0.48±0.07
0.48±0.07
0.48±0.07
14.1±1.0
14.0±1.0
13 to 18 years of age (n=2254) Age, years, mean ± SD
14.1±1.0
Weight, kg
50.5 (44.5–58.5)
52.1 (45.1–62.9)
48.5 (44.0–54.6)
Height, cm
159.0 (154.0–164.5)
162.2 (156.0–167.6)
157.0 (153.0–160.5)
19.7 (18.0–22.4)
19.8 (18.0–23.0)
BMI, kg/m2 SBP, mmHg
116.5 (108.0–125.0) 117.5 (108.0–125.0)
19.7 (18.0–22.0) 115.0 (107.5–122.5)
DBP, mmHg
70.0 (65.0–77.5)
70.0 (63.0–77.5)
70.3 (67.5–79.0)
SBPHR, mmHg/cm, mean ± SD
0.73±0.08
0.73±0.07
0.74±0.08
DBPHR, mmHg/cm, mean ± SD
0.45±0.06
0.43±0.06
0.46±0.06
Data are presented as 50th (25th to 75th) percentiles unless otherwise indicated. BMI Body mass index; DBP Diastolic blood pressure; DBPHR Diastolic blood pressure to height ratio; SBP Systolic blood pressure; SBPHR Systolic blood pressure to height ratio
parents or guardians of all subjects. The final sample consisted of 6837 students (3640 boys, 3197 girls), with an overall response rate of 89.1%. The present study was approved by the Ethics Committee of China Medical University (Shenyang, China). According to the standardized technique described by the American Heart Association (15), BP was measured by welltrained personnel from the bare right arm of participants, at the level of the heart, while participants remained seated with back support, after at least 5 min of rest. A calibrated mercury sphygmomanometer with appropriate cuff length was used. Participants were advised to avoid coffee, tea, stimulant foods, smoking and exercise for at least 30 min before the measurements. Two measurements were taken and averaged for analysis. All BP data were subsequently stratified using United States population-based percentiles (15). Normal BP was defined as an average systolic BP (SBP) and/or diastolic BP (DBP) 80 mmHg for adolescents. HBP (stages 1 and 2) was defined as average SBP and/or DBP ≥95th percentile, while average SBP and/or DBP >99th percentile plus 5 mmHg indicated stage 2 disease. Anthropometric data for all subjects, including height and body weight, were evaluated by specialists (cardiologists, internists and paediatricians) using standard protocols. Using a portable 66
stadiometer, the height of each subject (light clothing, no shoes) was measured to the nearest 0.5 cm. Body weight to the nearest 100 g was measured using a professional scale, and the body mass index was calculated (weight [kg]/height2 [m2]). SBPHR was calculated as SBP (mmHg)/height (cm) and DBPHR as DBP (mmHg)/height (cm). Data are expressed as mean ± SD or percentiles. Pearson’s or Spearman’s correlation coefficients were used to identify interrelating variables. Height was controlled when the relationships between age and BPHR were analyzed using partial correlation analysis. To test the value of the ratios (SBPHR and DBPHR) in detecting prehypertension and HBP (stages 1 and 2), ROC analysis was used. ROC curves plot sensitivity (true-positive ratio) by one minus the specificity (true-negative ratio) for a series of cut-off points established by SBPHR and DBPHR to the age-, sex- and height-specific SBP and DBP references, respectively. The area under the ROC curve (AUC) represents an overall measurement of performance of the test, with 1.0 representing a perfect test and 0.5 a test with no discriminating capacity. A test with an AUC of ≥0.85 was considered to be an accurate test (16). The optimal cut-off points were determined on the basis of ROC curve analysis where the sum of sensitivity and specificity achieved maximum, and prehypertension and HBP were defined using optimal cut-off points of SBPHR and DBPHR. Corresponding levels of sensitivity and specificity were then calculated. All data were analyzed using SPSS version 17.0 (IBM Corporation, USA), with statistical significance set at P99th + 5 mmHg
0.99 (0.97–0.996)
0.99 (0.99–1.00)
SBP ≥95th
0.94 (0.93–0.95)
0.98 (0.97–0.98)
DBP ≥95th
0.96 (0.95–0.97)
0.98 (0.98–0.99)
Table 5 Sensitivity and specificity of systolic blood pressure to height ratio and diastolic blood pressure to height ratio for diagnosis of high blood pressure in children and adolescents
All P90th and 99th + 5 mmHg
Thresholds, 0.81/0.50 0.77/0.50 0.84/0.54 0.83/0.53 0.87/0.63 0.87/0.59 mmHg/cm Sensitivity
0.87
0.94
0.92
0.91
0.98
0.94
Specificity
0.57
0.55
0.81
0.81
0.87
0.86
13 to 18 years of age (n=2254) Thresholds, 0.71/0.46 0.73/0.48 0.77/0.48 0.79/0.51 0.84/0.55 0.85/0.57 mmHg/cm
boys
Girls
boys
Girls
boys
Girls
Sensitivity
0.90
0.97
0.96
0.93
0.97
0.97
Cut-off points
0.81
0.77
0.84
0.83
0.87
0.87
Specificity
0.47
0.52
0.87
0.91
0.96
0.96
Sensitivity
0.76
0.91
0.90
0.87
1.00
0.93
Specificity
0.79
0.71
0.86
0.86
0.87
0.89
DbP >90th and 99th + 5 mmHg boys
Girls
Cut-off points
0.50
0.50
0.54
0.53
0.63
0.59
Sensitivity
0.96
0.94
0.97
0.92
1.00
1.00
Specificity
0.77
0.79
0.88
0.86
0.98
0.94
90th 90th percentile; 95th 95th percentile; 99th 99th percentile; DBP Diastolic blood pressure; SBP Systolic blood pressure
Table 3 presents the optimal cut-off points of SBPHR and DBPHR for identifying elevated SBP and DBP among children. The optimal thresholds for identifying SBP >99th percentile plus 5 mmHg were both 0.87 for boys and girls, while those for DBP >99th percentile plus 5 mmHg were 0.63 in boys and 0.59 in girls. The optimal thresholds for identifying SBP ≥95th percentile were 0.84 in boys and 0.83 in girls, while that for DBP ≥95th percentile were 0.54 in boys and 0.53 in girls. Sensitivities and specificities were lower for the identification of the level of SBP and DBP >90th and ≤95th percentiles. Table 4 presents the optimal cut-off points of SBPHR and DBPHR as well as corresponding sensitivity and specificity among adolescents. The optimal thresholds for detecting elevated BP at all levels were lower than those found among Paediatr Child Health Vol 18 No 2 February 2013
children. However, sensitivity and specificity in this age group were much higher. Table 5 presents the sensitivity and specificity of SBPHR and DBPHR for the identification of HBP status in both children and adolescents. The detection value in stage 2 HBP was found to be highest. Among adolescents, the sensitivities for detecting stage 2 HBP were both 97% in boys and girls, and the specificities were both 96% in boys and girls. The detection value in children was lower than that in adolescents, with sensitivities of 98% in boys and 94% in girls, and specificities of 87% in boys and 86% in girls for identifying stage 2 HBP.
disCussion
In the present cross-sectional study of 6837 children and adolescents, we found a relatively high overall prevalence of HBP (20.4%) and prehypertension (14.9%). The AUCs of SBPHR and DBPHR for detecting different levels of elevated BP were all >0.9 except for the range from the 90th to 95th percentile in both sexes across all ages. Among adolescents, SBPHR and DBPHR were good diagnostic markers for HBP, especially for stage 2 (sensitivities and specificities were >95% in both sexes). Although the specificities of BPHR for identifying HBP were not as high as sensitivities in children, the diagnostic efficiency remained acceptable. 67
Guo et al
As a consequence of epidemic paediatric obesity, paediatriconset HBP is on the rise in many areas. A dramatically increasing rate of HBP among children and adolescents was reported in the China Health and Nutrition Surveys, with an increase of prevalence from 7.1% in 1991 to 14.6% in 2004 (3). National Health and Nutrition Examination Surveys (NHANES) also indicated an increasing trend of BP in this segment of the population, showing that mean SBP and DBP increased by 1.4 mmHg and 3.3 mmHg, respectively, between the time periods from 1988 to 1994, and 1999 to 2000 (17). Consistent with our previous studies on adults, we observed a relatively high prevalence of hypertension in rural areas of northern China among children and adolescents. Based on the publication by Hansen et al (11), the underdiagnosis of HBP among children and adolescents has increasingly drawn attention. Many reasons related to the measurement and interpretation of BP may account for this high rate, to which the complicated and cumbersome diagnostic criteria contributed the most. Although using sex-, age- and height-specific percentiles to define childhood hypertension could achieve more precision and avoid overdiagnosis, its inconvenience and complexity limited its application in self-assessment and monitoring. To reduce future cardiovascular impact through early intervention, developing a practical, simple and highly accurate detection method is an urgenct necessity. In growing children and adolescents, height and age are highly correlated. Many studies have shown that both age and height are important determinants of HBP in young age groups (18-20). Height is also independently related to BP independent of age (21,22), highlighting the importance of height in defining paediatric hypertension. Therefore, it is reasonable to base this detection method on the use of BPHR, which showed strong correlation with SBP and DBP and weak correlation with age. Advantages of this particular method were addressed in greater detail by Lu et al (13). The present work compares favourably with the study by Lu et al (13), which was restricted to adolescents. Ratio (SBPHR and DBPHR) cut-off points for HBP in adolescents were similar, although the sensitivities and specificities we recorded were not quite as high. The outcomes were sufficient to validate this method, especially for identifying stage 2 HBP. We, therefore, advocate BPHR as an effective means of detecting HBP in adolescents. However, in this age group, we found that the specificities of BPHR for identifying prehypertension were relatively low in spite of acceptable sensitivities. To our knowledge, the present study was the first to examine BPHR values for the detection of HBP in children five to 12 years of age. All AUCs were >0.9 (except that of SBPHR for the level of the 90th to 95th percentiles) indicating good discriminating capacities. In identifying stage 2 HBP, the sensitivities were approximately 98% for boys and 94% for girls, and the specificities were approximately 87% for boys and 86% for girls. The AUC results for children, especially the specificities, were not as high as those observed among adolescents; however, we still suggest that this method may offer new detection criteria for childhood HBP, particularly for stage 2 HBP. It is possible to miss prehypertension using this method due to the low specificities in both sexes. Considering that the endocrine status and psychosocial states are dramatically different between the two sexes, we chose to perform sex-specific analyses. To be more precise and to facilitate comparison with previous studies (13,14), we also provided cut-off points for each sex. The strength of the present study was that we first examined this method among children based on a representative population 68
using a relatively large sample size. However, there are some limitations to the present study. First, participants in the study were not sufficiently ethnically diverse to facilitate extrapolation to all ethnic groups. Given the large differences in BP across ethnic groups (23), these new criteria need to be tested further in other ethnicities. Second, because the BP measurements were based on only one visit, the prevalence of HBP may be overestimated in the present study. BP tends to decrease in subsequent visits and HBP should be based on measurements taken over several visits (15). If possible, BP should be measured on multiple visits at different times.
ConCLusion
The ROC analysis in the present study confirmed satisfactory performance of BPHR for detection of HBP in children and adolescents, especially at stage 2. This novel method reduces hundreds of detection values to eight for each age group, with relatively high sensitivities and specificities. Therefore, we advocate the use of BPHR as a simple and practical means of detecting overt HBP (but not prehypertension) in these paediatric age groups.
reFerenCes
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