📊 Epidemiology — how common, and in whom
NHANES screening, which uses a single measurement session, labels a strikingly large share of children as having high BP: 15–19% of boys and 7–12% of girls. But confirmed hypertension, measured properly and repeatedly in a clinical setting, sits at about 3.5%, with persistently elevated BP another 2.2–3.5%.
Prevalence is higher in Hispanic and non-Hispanic African American children than in non-Hispanic white children, and higher in adolescents than in younger children. It has been rising over successive NHANES cycles, tracking the obesity epidemic.
🫀 What is blood pressure actually for?
Before asking what a normal pressure is, ask what pressure is doing. Arterial pressure exists to drive perfusion — and the hardest organ to perfuse is the one furthest above the heart. The brain sits at the top of a vertical column of blood, and gravity charges a toll on every centimetre of it.
≈ 0.78 mmHg for every centimetre of vertical height
Every centimetre the brain sits above the heart costs about 0.78 mmHg of perfusion pressure. To keep cerebral perfusion constant, a taller organism must generate a higher pressure at heart level. Not because it is older. Because it is taller.
🦒 The giraffe makes the point unarguable
An adult giraffe carries its head roughly 2 metres above its heart. At 0.78 mmHg per centimetre, that column costs about 155 mmHg of pressure before a single drop reaches the brain. So the giraffe runs a systemic pressure that would be a hypertensive emergency in any other mammal:
Roughly 300/200 at the heart yields about 100 mmHg at the brain — the same cerebral perfusion pressure a human enjoys. The giraffe is not hypertensive. It has exactly the pressure its anatomy demands. Its "normal" is set by the height of its column, not by its age. That is the identical logic the AAP tables apply to children, only over a range of centimetres rather than metres.
📏 Why height — and how much of it is really hydrostatics?
The hydrostatic argument predicts that BP norms should rise with height. The published tables confirm they do. But it is worth asking how much of the height gradient hydrostatics actually explains — and the answer is genuinely interesting.
Taking the 95th-percentile row and measuring the rise in BP from the 5th to the 95th height column at each age, then dividing by the height difference, gives the slope of BP on stature:
| Age (y) | Systolic (mmHg/cm) | Diastolic (mmHg/cm) | DBP ÷ SBP |
|---|---|---|---|
| 3 | 0.26 | 0.33 | 1.29 |
| 4 | 0.27 | 0.34 | 1.25 |
| 5 | 0.31 | 0.31 | 1.00 |
| 6 | 0.32 | 0.23 | 0.73 |
| 7 | 0.32 | 0.16 | 0.50 |
| 8 | 0.33 | 0.15 | 0.46 |
| 9 | 0.31 | 0.09 | 0.31 |
| 10 | 0.35 | 0.07 | 0.19 |
| 11 | 0.39 | 0.04 | 0.11 |
| 12 | 0.41 | 0.04 | 0.10 |
| 13 | 0.36 | 0.10 | 0.28 |
| 14 | 0.30 | 0.18 | 0.59 |
| 15 | 0.25 | 0.19 | 0.74 |
| 16 | 0.24 | 0.17 | 0.72 |
| Mean 3–16 | 0.32 | 0.17 | 0.54 |
Now the test. A hydrostatic column is a uniform offset — it adds the same pressure to the whole waveform, systolic and diastolic alike. So if hydrostatics were the entire explanation, the systolic and diastolic slopes should be equal, and the ratio in that last column should sit at 1.00.
In early childhood it very nearly does. At ages 3–5 the ratio runs 1.29, 1.25, 1.00 — the height gradient behaves almost exactly like a uniform pressure offset, which is what a hydrostatic column looks like. Then it decouples. From age 6 the systolic slope climbs while the diastolic slope collapses, bottoming near 0.04 mmHg/cm in the pre-pubertal years before partially recovering. Averaged across ages 3–16 the systolic slope is 0.32 and the diastolic only 0.17 — a ratio of 0.54.
So the honest reading is two-part. Hydrostatics is the floor — it is why height belongs in the equation at all, and it accounts for essentially the whole diastolic gradient and roughly two-thirds of the systolic one. The residual systolic gradient is maturation — stroke volume, arterial stiffness, sympathetic tone and pubertal development, all of which track height closely during the growth spurt. Height earns its place in the table twice over: once as a physical column, once as the best available proxy for somatic maturity.
⚖️ Why not weight?
The obvious objection: bigger children have higher pressures, so why not index to weight or BMI? The answer is the sharpest concept in this entire topic.
Height is largely fixed by genetics and maturation and is not moved by the pathology you are screening for. Weight is the pathology. That distinction is not merely theoretical: the 2017 guideline made it operational by excluding children with overweight and obesity (BMI ≥ 85th percentile) from the normative sample entirely. The 2017 percentiles describe what a normal-weight child's pressure looks like, which is exactly the comparator you want when assessing a child with obesity. It is also why 2017 values run roughly 2–3 mmHg below the older Fourth Report figures at the same age, sex and height.
🍔 Obesity and the cardiometabolic cluster
Hypertension prevalence in youth with overweight and obesity ranges from 3.8% to 24.8%, rising in a graded fashion with adiposity — and the same graded relationship holds for waist circumference. This is why the guideline asks for a BP at every encounter in a child with overweight or obesity, rather than annually.
Blood pressure rarely arrives alone. Obesity-associated hypertension travels with dyslipidaemia and disordered glucose metabolism, and the combination appears to be worse than the sum of its parts. In the Strong Heart Study, American Indian adolescents carrying multiple cardiometabolic risk factors had markedly more target-organ damage than those without:
| Finding | Multiple risk factors | Without |
|---|---|---|
| Left ventricular hypertrophy | 43.2% | 11.7% |
| Left atrial dilation | 63.1% | 21.9% |
Both obesity and hypertension independently drove these changes. In a 15-year-old, left ventricular hypertrophy is not an abstraction — it is target-organ damage with six decades still to run. This clustering is the pediatric entry point into cardiovascular-kidney-metabolic (CKM) thinking: the organs fail together because the drivers are shared.
🧬 Primary versus secondary — who actually needs a workup?
The old teaching was that hypertension in a child is secondary until proven otherwise. That has flipped. Primary hypertension is now the predominant diagnosis among hypertensive children and adolescents seen in US referral centres. The clinical task is no longer "find the secondary cause" but "decide who plausibly has one."
Points toward primary
- Age ≥ 6 years
- Positive family history in a parent or grandparent
- Overweight or obesity
- Systolic predominant elevation
- Normal history and physical examination
Points toward secondary
- Age < 6 years
- Very high BP, or stage 2 at presentation
- Diastolic predominant elevation
- No obesity, no family history
- Any red-flag finding on examination
The guideline turns this into an explicit permission to not investigate. A child ≥ 6 years with a positive family history, overweight or obesity, and no history or examination findings suggesting a secondary cause does not require an extensive secondary evaluation. That is a deliberate move away from reflexive testing.
🪵 Pediatric-specific causes by age
Renal parenchymal disease and renal structural abnormalities dominate: together they accounted for 34–79% of secondary hypertension across single-centre series. The differential shifts markedly with age.
Neonate / infant
- Renal artery or venous thrombosis (umbilical catheter)
- Congenital renal disease, ARPKD
- Coarctation of the aorta
- Bronchopulmonary dysplasia
- Iatrogenic — steroids, inotropes
1–6 years
- Renal parenchymal disease, scarring from reflux
- Renovascular disease, fibromuscular dysplasia
- Coarctation
- Wilms tumour, neuroblastoma
- Monogenic forms — Liddle, apparent mineralocorticoid excess
6–12 years
- Renal parenchymal disease, glomerulonephritis
- Renovascular disease
- Primary hypertension begins to dominate
- Endocrine — thyroid, CAH, Cushing
- Obstructive sleep apnoea
Adolescent
- Primary hypertension — most common
- Renal parenchymal disease
- Substances — stimulants, OCPs, NSAIDs, energy drinks, anabolic steroids
- Obstructive sleep apnoea
- Phaeochromocytoma, hyperaldosteronism
🫀 Coarctation — the one you cannot afford to miss
Coarctation deserves separate billing because it is mechanically obstructive, surgically correctable, and missable by a completely routine BP check — a single right-arm reading in a coarctation patient can look merely "high", or even normal.
Examination
- Four-limb blood pressures
- Simultaneous radial and femoral palpation for delay
- Interscapular or left infraclavicular murmur
- Differential cyanosis in the neonate
Why the right arm
- The guideline specifies the right arm for all BP measurement
- Consistency with the reference tables
- A left-arm reading can be falsely low in coarctation if the lesion involves the left subclavian origin
After repair
- Repair does not end the story — late and masked hypertension are common
- The guideline calls for ABPM after coarctation repair to detect hypertension including masked hypertension (grade B, strong)
- Office readings alone will under-detect it
🔬 Evaluating for a secondary cause
When history, examination or the pattern of hypertension points away from primary disease, the first-line evaluation is aimed squarely at the kidney, then widens on the basis of clues.
| Tier | Tests | Looking for |
|---|---|---|
| All children | Urinalysis, chemistry panel and creatinine, lipid profile, renal ultrasound in those <6 y or with abnormal urinalysis or renal function | Renal parenchymal and structural disease |
| With obesity | HbA1c, fasting glucose, ALT/AST, lipids | The cardiometabolic cluster |
| Directed | Renin and aldosterone, plasma or urine metanephrines, thyroid studies, cortisol testing, drug screen, polysomnography | Endocrine causes, phaeochromocytoma, OSA, exogenous agents |
| Imaging | Renal artery imaging (CTA, MRA or Doppler), echocardiography | Renovascular disease, coarctation, LVH as target-organ damage |
📋 Applying it
📚 Key references
- Flynn JT, Kaelber DC, Baker-Smith CM, et al. Clinical Practice Guideline for Screening and Management of High Blood Pressure in Children and Adolescents. Pediatrics. 2017;140(3):e20171904. PMID 28827377.
- Aalkjær C, Wang T. The Remarkable Cardiovascular System of Giraffes. Annu Rev Physiol. 2021;83:1–15. PMID 33167747.
- National High Blood Pressure Education Program Working Group. The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents. Pediatrics. 2004;114(2 Suppl):555–576. PMID 15286277. Superseded — cited for historical comparison only.
- CDC 2000 Growth Charts, stature-for-age and length-for-age LMS parameters. National Center for Health Statistics.