Hypertension in Children and Adolescents

1

How is hypertension defined in children and adolescents?

The definition of hypertension in adults is based on data from large clinical trials, which show that as blood pressure (BP) rises, the risk of cardiovascular endpoints such as stroke, myocardial infarction, and mortality increases. As these events are rare in the pediatric age group, a statistical definition has been adopted that is based upon the distribution of BPs in healthy children, with BP values at the upper end of the distribution (≥90th percentile) considered abnormal. In 2017 the American Academy of Pediatrics (AAP) issued an updated clinical practice guideline for the evaluation and management of childhood hypertension. This new guideline included new normative BP data based only upon children of normal weight, as well as revised BP categories. The new normative BP values (available at https://pediatrics.aappublications.org/content/140/3/e20171904.long ) are generally 2 to 3 mm Hg lower than the values previously in use. This guideline for the first time also adopted adult BP categories for adolescents at least 13 years of age. The categories can be summarized as follows:

• Normal BP: BP <90th percentile for age, sex, and height; or <120/<80 mm Hg for adolescents ≥13 years old;

• Elevated BP: BP ≥90th percentile and <95th percentile for age, sex, and height; or 120 to 129/<80 mm Hg for adolescents ≥13 years old;

• Hypertension: BP >95th percentile for age, sex, and height; or ≥130/80 mm Hg for adolescents ≥13 years old. Hypertensive-level BP is further staged as follows:

  • Stage 1 hypertension: BP >95th percentile for age, sex, and height up to the 95th percentile + 11 mm Hg; or 130 to 139/80 to 89 mm Hg for adolescents ≥13 years of age; and

  • Stage 2 hypertension: BP ≥95th percentile +12 mm Hg for age, sex, and height; or >140/90 mm Hg for adolescents ≥13 years of age.

Other organizations, including Hypertension Canada and the European Society of Hypertension (ESH), have also issued guidelines for evaluation of children and adolescents with high BP; their definitions of the different BP categories are roughly similar to those in the AAP guideline. The major differences are that these other guidelines were issued prior to the availability of the revised American normative BP data and used different static cut-points for adolescents.

2

How common is hypertension in children and adolescents?

Initially, the thresholds used for defining hypertension in the young were the same as those used in adults. Unsurprisingly, hypertension was found to be exceedingly rare in young children but could affect up to 2% of adolescents. Later screening studies applied population-based percentiles of BP as the threshold for diagnosis (see earlier) and confirmed that less than 2% of children had hypertension. These screening programs also demonstrated the importance of performing repeated measures of BP before diagnosing hypertension: studies that used just one BP determination found significantly higher “prevalences” of hypertension than studies in which repeated measurements were obtained.

Over the past decade, however, the childhood obesity epidemic has resulted in an increased prevalence of hypertension in the young. Multiple studies have demonstrated an increased prevalence of hypertension among obese children—as high as 4.5%—compared with nonobese children. Indeed, it is now generally accepted that the prevalence of elevated BP has reached 10%, and the overall prevalence of hypertension is nearly 4%. Of significant concern in the United States is that this increase has been much greater in non-Hispanic Black and Mexican American children than in White children. Similar findings have been seen in screening studies performed in other countries, including China, the Seychelles, and Iceland. Finally, with the publication of the new normative data in the AAP guideline, recent studies have shown even greater rates of elevated BP and hypertension both in the United States and abroad.

3

What are the causes of hypertension in children and adolescents?

Historically, hypertension in children and adolescents was considered secondary in origin, and the diagnosis of primary hypertension was made only after an exhaustive diagnostic evaluation. As discussed previously, this may have been related to the lack of normative childhood BP data, which required the use of adult hypertension cut-points to identify high BP in children as well. If an 8-year-old child was only diagnosed with hypertension if their BP was greater than 140/90, then of course secondary causes would be commonly found given that 140/90 is now known to be well above the normal distribution of BP in 8-year-old children. This began to change in the late 1970s as large-scale population-based screening studies began to elucidate what constitutes normal and high BPs among children and adolescents. Further refinement of the normative data as described in question 1 has established much different—and lower—thresholds for diagnosing hypertension in the young, resulting in a larger number of children identified with high BP and reducing the proportion with severe hypertension likely to be secondary in origin.

The other major change since the earliest efforts to understand childhood hypertension has been the rapid increase in childhood obesity (see later). Given this, it is now clear that the predominant form of hypertension in children, at least those older than 6 years of age, is primary hypertension with secondary causes accounting for a smaller proportion of all hypertension. In fact, at least one recent multicenter study conducted in the United States demonstrated that primary hypertension was found in 90% of all children and adolescents referred to tertiary pediatric centers. This means that most children and adolescents with hypertension do not need the exhaustive evaluation for secondary forms of hypertension that was previously recommended. As discussed further in question 7, only children with characteristic findings on history and physical examination, or with markedly abnormal screening test results, should be evaluated for secondary causes.

4

What factors contribute to the development of childhood primary hypertension?

The two factors that appear to be most influential in children and adolescents with primary hypertension are family history and obesity. In multiple cases series, the majority of children with primary hypertension had a parent or grandparent with hypertension. Twin studies have also confirmed the familial tendency toward hypertension, with heritability estimates of around 50% to 60%.

Obesity is well-known to contribute to the development of hypertension via a variety of mechanisms, including activation of the sympathetic nervous system, activation of the renin-angiotensin-aldosterone system, and impaired renal sodium handling. Screening studies conducted over the past two decades in the United States and elsewhere have shown that the prevalence of hypertension in children with body mass index at the 95th percentile or above is several times higher than among children with normal weight. Most alarmingly, the steady increase in obesity rates among children in the United States, Mexico, Chile, India, China, and many other countries has been accompanied by increases in the prevalence of elevated BP and hypertension in youth, which is likely to be followed by increased rates of adult cardiovascular disease.

Recently, another important factor has emerged as a likely contributor to the development of primary hypertension in the young—premature birth. It has become increasingly clear that hypertension occurs more commonly among children born early compared with those born at term. Mechanisms are unclear but likely include reduced nephron endowment and epigenetic changes in DNA function induced by an adverse intrauterine environment. With the increased survival of premature infants as young as 24 weeks’ gestation, the importance of prematurity as a contributing factor to pediatric hypertension is likely to increase. Given this, it is important to obtain a full birth history when evaluating children and adolescents with suspected hypertension (see later).