PEDIATRICS Vol. 122 No. 2 August 2008, pp. 238-242 (doi:10.1542/peds.2007-2776)
ARTICLE |
Blood Pressure Variability and Classification of Prehypertension and Hypertension in Adolescence
a Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania
b Nemours Cardiac Center, A. I. duPont Hospital for Children, Wilmington, Delaware
c Division of Pediatric Nephrology and Hypertension, University of Texas Medical School, Houston, Texas
d Channing Laboratory, Harvard Medical School, Boston, Massachusetts
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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OBJECTIVE. There is little information in pediatrics on the persistence of the prehypertension and hypertension classifications or on the progression of prehypertension to hypertension. This study aimed to examine those issues.
METHODS. An analysis of data from the National Childhood Blood Pressure database was conducted to examine the longitudinal blood pressure outcomes for adolescents classified after a single measurement of blood pressure. Adolescent subjects (N = 8535) for whom serial single blood pressure measurements were obtained at intervals of 2 years were identified. Subjects were stratified according to blood pressure status at the initial measurement, as having normotension, prehypertension, or hypertension.
RESULTS. Among subjects designated as having prehypertension (n = 1470), 14% of boys and 12% of girls had hypertension 2 years later. Among subjects designated as having hypertension, 31% of boys and 26% of girls continued to exhibit hypertension, and 47% of boys and 26% of girls had blood pressure values in the prehypertensive range. Regression models showed no significant effect of race on blood pressure changes but significant effects of initial BMI and changes in BMI.
CONCLUSIONS. These data indicated that the rate of progression of prehypertension to hypertension was 
7% per year. Prehypertension can be predictive of future hypertension and may benefit from preventive interventions, especially lifestyle changes.
Key Words: blood pressure • hypertension • obesity • adolescents
Abbreviations: BP—blood pressure
The fourth report on high blood pressure (BP) in children and adolescents by the National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents1 introduced the diagnosis of prehypertension in the assessment of cardiovascular risk in childhood. Children with BP values consistently above the 90th percentile for age, gender, and height and adolescents with BP values above 120/80 mm Hg but below the threshold for hypertension meet the criteria for this diagnosis. For both hypertension and prehypertension, multiple BP measurements are required before an established diagnosis can be confirmed. It is predicted that, among adults with prehypertension, as many as 10% per year develop hypertension, which supports recommendations to encourage lifestyle behavior changes that can prevent increases in BP.2 In a recent clinical trial that carefully selected patients with repeated measurements of systolic BP between 130 and 139 mm Hg and/or diastolic BP between 85 and 89 mm Hg, it was reported that the rate of progression to stage 1 hypertension, without pharmacologic intervention, was 16% per year.3
There is little information on the time course for children with prehypertension to develop hypertension. Because BP increases with age and the prehypertension cutoff point is fixed at 120/80 mm Hg by middle adolescence, compared with percentile-based values at younger ages, it is likely that many youths develop hypertension.4 Increasing obesity, large sodium intakes, and decreases in physical activity that occur in adolescence may contribute to this rise.5–7
The National Childhood Blood Pressure database, a collection of population-based BP data for children from several epidemiological studies, was used to develop the age-, gender-, and height-specific BP percentile values used in the fourth report.1 More than 8000 boys and girls, 13 to 15 years of age, in the database had initial BP measurements and BP measurements obtained 2 and 4 years later. The purpose of this study was to determine the longitudinal BP outcomes for adolescents designated as having prehypertension. The effects of age, gender, and BMI on BP outcomes were also assessed.
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METHODS |
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Data from the National Childhood Blood Pressure database were examined. A detailed description is provided in the fourth report.1 Among the 11 individual studies of BP in childhood in the database, the data used in this analysis were obtained from the studies that included adolescents with repeat BP measurements obtained at intervals of 2 and 4 years. The original sources of these data were in Dallas, Texas,8,9 and Bogalusa, Louisiana.10–12 Table 1 provides a description of the childhood BP data sources from which the adolescent data used in these analyses were drawn. BP was measured with different study protocols in each study. However, all studies used auscultation with mercury manometers and averaged
2 readings for determination of BP values. Information on race, age, gender, height, and weight were available for each participant.
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The adolescent sample used in this analysis included 8533 boys and girls, initially 13 to 15 years of age. The racial composition of the cohort was as follows: white, 39%; black, 51%; Hispanic, 10%. Baseline BP levels, according to gender, age, and height, for this adolescent sample were as represented in the fourth report.1 In addition to adolescents who underwent repeated BP measurements 2 years later, 2675 of those who were 13 years of age at the initial assessment underwent BP measurements at 17 years of age. BP status (normal BP, prehypertension, or hypertension) was determined according to age, gender, and height percentiles at the initial and subsequent measurements (2 years and 4 years later) according to the criteria of the fourth report, with the exception that the classification was based on a single measurement, rather than serial measurements.1 Prehypertension was classified as BP that was of
90th percentile for systolic or diastolic BP or 120/80 mm Hg (whichever was lower) but below the threshold for hypertension (95th percentile). Hypertension was classified as systolic or diastolic BP of 95th percentile. Table 2 provides the BP values (from the fourth report1) for prehypertension and hypertension for adolescents 13, 15, and 17 years of age. In Table 2, 120 mm Hg was entered when the 90th percentile for systolic BP was >120 mm Hg, and 80 mm Hg was entered when the 90th percentile for diastolic BP was >80 mm Hg. Although only the 10th, 50th, and 90th height percentiles are provided in Table 2, gender-specific height percentiles were used to determine the BP classification for each participant. Contingency table analyses were used to assess (separately for boys and girls) the relationship between baseline BP status and BP status 2 and 4 years later. Multivariate regression analysis was performed to relate the change in BP z[r] scores to BMI and BMI changes over a 2-year period by using a model for BP z score at 2 years based on the z score at baseline, age, race, initial BMI, and change in BMI (year 2 minus baseline).
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RESULTS |
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Table 3 presents BP status at baseline and at the 2-year follow-up evaluation for boys (n = 4147) and girls (n = 4386). Of those designated as having prehypertension at the initial visit (882 boys and 588 girls), 14% of boys and 12% of girls were designated as having hypertension at the 2-year follow-up evaluation. Prehypertension persisted in 50% of boys and 24% of girls who were initially designated as having prehypertension. Among boys, the conversion of prehypertension to hypertension (14%) was significantly greater than the conversion of normotension to hypertension (5%) (
2 = 70.21; P < .001). The difference between these 2 groups was also significant among girls (2 = 51.92; P < .001). Table 4 presents 4-year follow-up data for subjects who were examined initially at 13 years of age. Of those who were designated as having prehypertension at 13 years of age, 15% of boys and 14% of girls were designated as having hypertension at 17 years of age. The conversion of prehypertension to hypertension (15%) was significantly greater than the conversion of normotension to hypertension (5%) (2 = 25.44; P < .001). The difference between these 2 groups was also significant among girls (2 = 18.38; P < .001).
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Among adolescents initially designated as having hypertension, 77% of boys (n = 362) and 53% of girls (n = 224) had either prehypertension or hypertension 2 years later. Among those designated as having hypertension at 13 years of age, 83% of boys (n = 121) and 54% of girls (n = 89) had either prehypertension or hypertension 4 years later, at 17 years of age.
Regression analyses were performed with data for the sample of adolescents designated as having prehypertension at the initial examination, to examine the effects of age, race, and BMI on systolic BP z score changes (Table 5). There were significant effects of initial BMI and change in BMI on future systolic BP z scores for both boys and girls (P < .001). For girls, there was also a significant positive effect of age (P < .001). No significant effects were seen for diastolic BP z score changes in boys; for girls, there was a significant effect of change in BMI (P = .011). No significant effects of ethnicity were found for either systolic or diastolic BP z score changes for either boys or girls.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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An examination of national childhood BP data indicated that
20% of adolescent boys and 13% of adolescent girls met the criteria for prehypertension with a single BP measurement. Analysis of the data for subjects with measurements obtained 2 years later demonstrated that, in adolescence, the rate of progression from prehypertension to hypertension was 7% per year. High BMI at initial presentation and increasing BMI during the follow-up period predicted sustained BP elevations. These data support the identification of prehypertension. Adolescents with prehypertension would derive the most benefit in prevention of adverse outcomes resulting from additional BP increases. Prehypertension is a BP classification that was first described in the seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.2 The rationale for this category is related to the fact that risk associated with elevated BP is continuous and graded. Among adults, the risk for cardiovascular events increases beginning at a BP level of 115/75 mm Hg, and the risk doubles with every 20-mm Hg increment.13 Compared with those with normotension, adults with prehypertension are known to have a higher prevalence of other cardiovascular disease risk factors.14–16 Risk factors that typically are associated with prehypertension, including BMI, lipid levels, and smoking, are modifiable and may be responsive to certain lifestyle changes. The prevalence of prehypertension tends to be higher among young adults, compared with older adults.15 Because both BP level and hypertension prevalence increase with age, individuals with prehypertension progress to the hypertension threshold. Lifestyle changes that modify BP and associated risk factors may delay the need for pharmacologic intervention or successfully treat prehypertension.1,2
Among adolescent boys, 21% met BP criteria for prehypertension at the initial examination; among adolescent girls, 13% met BP criteria for prehypertension. A limitation of this analysis is the use of a single BP measurement for classification. A classification that is based on a single measurement overestimates the prevalence of hypertension and prehypertension. BP tends to decrease in subsequent visits because of accommodation effect and regression to the mean.1,17 The variability of BP classification observed over 2-year and 4-year intervals in the analyses of these data confirms the recommendation to measure BP multiple times. Among adults, BP values at prehypertensive and hypertensive levels represent high-risk BP values.13–16 Of the adolescents with high-risk BP values, including those designated as having prehypertension or hypertension combined at the initial examination, 68% of boys and 43% of girls had either prehypertension or hypertension 2 years later; of the combined high-risk group at the initial examination, 77% of boys and 46% of girls had prehypertension or hypertension 4 years later. However, without repeated BP measurement sessions for participants classified as having hypertension in a single BP measurement session, it is not possible to make a clinical diagnosis of hypertension.
It is also of note that the regression to normal BP in subsequent BP measurements was greater in girls than boys. The prehypertension threshold for abnormal BP is 120/80 mm Hg for both boys and girls. However, the mean BP according to age among all adolescent girls is lower than the mean BP according to age among all adolescent boys. Therefore, greater regression to the mean would be expected among adolescent girls than among adolescent boys. This would be manifested by a greater conversion to normotension from baseline prehypertension in adolescent girls, compared with adolescent boys. McNiece et al18 conducted a cross-sectional study of the prevalence of prehypertension and hypertension among adolescents, using 3 separate BP measurement sessions. They also reported lower prevalence rates of both prehypertension and hypertension in girls, compared with boys. Another gender effect detected was the effect of age on the change in systolic BP z scores in girls but not boys (Table 5). We do not have an explanation for this result. The age range in this adolescent sample was very narrow, and the result could be no more than a spurious effect.
Repeated BP measurements are necessary for diagnosis of hypertension and ascertainment of risk in asymptomatic well children and adolescents. Hansen et al19 used electronic medical records from well-child care visits for a cohort of 14 187 children and adolescents (age range: 3–18 years) to determine the prevalence rates of prehypertension and hypertension. With the criterion of elevated BP on 3 well-child visits, the prevalence of hypertension was 3.6% and the prevalence of prehypertension was 3.4%. The primary purpose of that study was to determine the frequency, in children and adolescents, of hypertension and prehypertension (verified with repeated BP measurements) that had not been diagnosed by clinicians, and the authors did not provide data on the prevalence of single elevated BP measurements. In a cross-sectional study that focused on adolescent high school students, the prevalence rates of prehypertension and hypertension in a cohort of 6790 adolescents (age range: 11–17 years) were determined by using the recommended repeated measurements of BP. The study was conducted in schools in Houston, Texas, and repeated measurements (obtained at separate sessions) were obtained for at-risk adolescents. With repeated BP measurements, the prevalence of prehypertension in adolescents was 15.7% and the prevalence of hypertension was 3.2%.18 Those prevalence figures, verified with repeated BP measurements, are comparable to the data presented in this report. Despite the intrinsic variability of BP measurements, the best predictors of future BP are initial BP, initial BMI, and changes in BMI, as documented in many studies tracking BP from childhood to adulthood.20,21
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CONCLUSIONS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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In clinical practice, childhood prehypertension is recognized in the context of a primary care health maintenance visits. The fourth report recommends lifestyle intervention for prehypertension and follow-up BP monitoring.1 With adherence, weight control and increased physical activity are associated with long-term beneficial effects on BP.7,22
Children with prehypertension have a significant risk for development of hypertension, even within 2 to 4 years. Both overweight and excessive weight gain contribute to progression toward hypertension. Identification of adolescents with prehypertension and initiation of lifestyle changes may affect this trend.
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ACKNOWLEDGMENTS |
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This work was supported by grant HL40619 from the National Heart, Lung, and Blood Institute.
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FOOTNOTES |
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Accepted Dec 7, 2007.
Address correspondence to Bonita Falkner, MD, Department of Medicine, Thomas Jefferson University, 833 Chestnut St, Suite 700, Philadelphia, PA 19107. E-mail: bonita.falkner{at}jefferson.edu
The authors have indicated they have no financial relationships relevant to this article to disclose.
| What's Known on This Subject Concurrent with the childhood obesity epidemic is an increase in obesity-related disorders, including hypertension. Children with elevated blood pressure could be at risk for hypertension.
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| What This Study Adds This study provides data demonstrating that single elevated blood pressure measurements identify a group of adolescents who are at heightened risk for subsequent hypertension.
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PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics
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