The main methodological differences involve the criteria for diagnosis and classification of HTN. This is due to: (a) differences in reference values; (b) difference in the age used to apply the adult criteria for definition of HTN, replacing the traditional approximation by BP percentiles and (c) differences in the classification of HTN.

• a)

  The reference values for BP come from the same source in both guidelines, the 2004 US Task Force cohort.5 While the European guidelines maintain the percentiles of the original cohort, the United States guidelines calculate the percentiles based only on children with normal weight. The exclusion of children with overweight or obesity, which were included in the original cohort, was founded on the risk of bias that could lead to underdiagnosis of HTN.

• b)

  For the diagnosis of HTN, both guidelines use BP percentiles for age, sex and height, until the age of 16 years in the European guidelines and the age of 13 years in the United States guidelines. Starting from these ages, adult criteria are applied to define HTN: 140/90mmHg in the European guidelines10 and 130/80mmHg in the United States guidelines,11 thresholds that are not free from controversy (Table 1).12,13

  Table 1.

  Definition of normal BP and HTN in children and adults.

  	European guidelines7		United States guidelines8
  	<16 years	≥16 years and adults	<13 years	≥13 years and adults
  Normal BP		<130/85		<120/<80
  Normal-elevated	≥P90th to	130–139/85–89	≥P90th to*	120–129/<80
  HTN
  Stage 1	≥P95th to P99th+5mmHg	140–159/90–99	≥P95th to <P95th+12mmHg¥	130/80 to 139/89
  Stage 2	>P99th+5mmHg	160–179/100–109	≥P95th+12mmHg§	≥140/90
  Isolated systolic	SBP≥P95th and DBP<P90th	SBP≥140 and DBP<90	Not discussed

  P90th, 90th percentile; P95th, 95th percentile; P99th, 99th percentile.

  * or 120/80, whichever is lowest.

  ¥ or 130/80 and 139/89, whichever is lowest.

  § or 140/90, whichever is lowest.
• c)

  The definitions of stages 1 and 2 also differ between the European and the United States guidelines, as the latter applies the criteria of the published guidelines for the adult population (Table 1).7,8

The choice of age 16 years in the European guidelines is based on the fact that in adolescents aged 16 and 17 years, with the exception of males aged 17 years at or above the 95th percentile for height, all the specific values for the 95th percentile for BP are below the threshold used to define HTN in adults. When adolescents become adults, this difference may lead to an adolescent previously considered to have HTN to be considered a normotensive adult on turning 18 years old due to discrepancies in definition criteria.

The United States guidelines lower the age for application of adult BP criteria to 13 years. It could be argued that simplifying this criterion for the diagnosis of HTN would facilitate the identification of children at higher risk of cardiovascular disease. When the threshold of 130mmHg is applied at the age of 13 years, it is below the 95th percentile for age, sex and height in male adolescents, whereas the opposite is true of female adolescents, in whom the 95th percentile does not reach 130mmHg in any instance.

The first consequence of these differences involves the prevalence of HTN. The United States guidelines result in a greater proportion of children considered to have HTN, although not in a greater proportion needing pharmacological treatment.

This greater prevalence leads to increases in:

• a)

  The patients requiring clinical monitoring.

• b)

  The use of 24-h ABPM, due to the recommendation that “ABPM should be performed for the confirmation of HTN in children and adolescents with office BP measurements in the elevated BP category for 1 year or more or with stage 1 HTN over 3 clinic visits (Grade C, moderate recommendation).”8 Both guidelines7,8 recognise the usefulness of ABPM for the identification of white-coat HTN and masked HTN and that it is the sole method available for diagnosis of nocturnal HTN, which carries risks that are independent of the daytime ambulatory and office BP values. The reported frequency of white-coat and masked HTN varies as a result of the office and ambulatory BP criteria used to establish the diagnosis. In this context, the lower office BP values established by the United States guidelines for the definition of HTN will result in a marked increase in the proportion of individuals with white-coat HTN, as the reference used to define HTN by the ABPM method continues to be the distribution tables obtained for the European population.14

• c)

  Performance of diagnostic tests to assess early organ damage. The timing of the evaluation of potential target organ damage has considerable clinical relevance. The assessment of left ventricular mass continues to be the key in the investigation of early signs of organ damage. Children and adolescents with HTN may have left ventricular hypertrophy even in the early stages of disease,7,8 and delaying evaluation may lead to errors in risk stratification. The European guidelines recommend monitoring target organ damage after HTN is diagnosed and considers its presence as an indication for initiating pharmacological treatment; the United States guidelines recommend assessment of left ventricular mass only at the time that pharmacological treatment is considered. Thus, the European guidelines promote the assessment and detection of target organ damage as a way to establish the need of pharmacological treatment in children and adolescents with HTN.

• d)

  The ongoing debate on the BP targets to pursue in treatment is also considered in the recommendations of both guidelines. In children, the evidence supporting specific BP targets is scarce, and there is also uncertainty regarding the specific impact of drugs on cardiovascular and renal outcomes. In the absence of prospective, long-term studies on the impact of different BP levels in intermediate or final cardiovascular or renal goals, the 95th percentile is considered the BP target, as this was the threshold used to define HTN in children and adolescents, although lowering BP below the 90th percentile would be preferable as long as the treatment is well tolerated. In individuals aged 16 years or more, the European guidelines recommend establishing targets using the cutoff for clinically significant BP in adults, that is, of less than 140/90mmHg, without discouraging the goal of less than 130/80mmHg. Conversely, the United States guidelines recommend reducing BP to less than 130/80mmHg starting at the age of 13 years.

• e)

  When it comes to patients with chronic kidney disease (CKD), the European guidelines recommend a BP target below the 75th percentile in children with nonproteinuric renal disease and a BP target below the 50th percentile in those with proteinuric disease.15 This recommendation differs from the United States guidelines, which recommend a BP target below the 50th percentile in nonproteinuric patients, too, although there is no evidence that this measure provides additional protection against renal events in nonproteinuric CKD.16

Finally, isolated systolic HTN, the most frequent type of HTN in adolescents, has been specifically considered by the European guidelines7 (Table 1) but not the United States guidelines.8 In a high proportion of cases, elevation of SBP with a normal DBP is associated with normal BP in the aortic root. Various mechanisms may be involved in these discrepancies, but this phenomenon nevertheless affects clinical decision-making. At present, we accept the recommendation that patients with isolated systolic HTN undergo measurement of central aortic BP by indirect, non-invasive methods, as this allows the detection of left ventricular mass abnormalities. In patients with normal central BP and left ventricular mass, it is possible to apply a watchful waiting approach without initiating treatment.17