Journal of Hypertension:
Reference blood pressure values in childhood: an issue to be solved
Pediatric Department, Consorcio Hospital General, University of Valencia, CIBER Fisiopatología Obesidad y Nutrición (CB06/03), Instituto de Salud Carlos III, Valencia, Spain
Correspondence to Empar Lurbe, MD, Department of Pediatrics, Consorcio Hospital General, University of Valencia, Avda Tres Cruces s/n., 46014 Valencia, Spain. Fax: +34 96 3862647; e-mail: email@example.com
The goal of blood pressure (BP) measurement in children and adolescents is to provide strategies for promoting cardiovascular health. It is well accepted that BP values in children represent one of the most important measurable markers of cardiovascular risk later in life. The accurate identification of children at risk at the earliest possible age would give healthcare providers the opportunity to initiate preventive measures, thereby reducing the chance of developing end-organ damage and its attendant morbidity and mortality. The assessment of BP was firmly recommended in children and adolescents in the course of routine healthcare by the European Society of Hypertension (ESH) guidelines for management of high BP in children and adolescents . Furthermore, the ESH guidelines proposed 3 years as the most convenient age to begin.
Evaluation of a BP measurement in a child first requires determination of the child's height percentile, and then comparing the child's BP level to the childhood BP tables according to the sex, age, and height percentile. Because the normal range of BP shifts with normal growth and development, the BP levels that denote high BP will change accordingly. By widespread convention, the 95th BP percentile of a reference population defines hypertension and the 90th BP percentile defines high-normal BP.
The ESH guidelines stated that due to the large amount of data available, the Task Force for Blood Pressure in Children  is still the study of reference for BP percentiles, using the auscultatory method, even though they do not refer to a European population. However, the recent banning of mercury devices in the European Community will undoubtedly favour the development of oscillometric devices, but it is also true that the auscultatory method can continue to be used with manometers other than the mercury one. It would be convenient, however, to start assembling reference BP data using validated oscillometric devices .
After the recommendations of the ESH the first European BP reference oscillometric data have become available in 2011 from a large cohort of German schoolchildren . BP percentiles from 12 199 German non-overweight children and adolescents aged 3–17 years were calculated. Compared with the Fourth Report the 90 and 95th percentiles were mostly lower. The lower BP values for 90th and 95th percentiles were expected due to the fact that the Fourth-Report BP references did not exclude overweight children.
In the current issue of the Journal of Hypertension, Kulaga et al.  provide oscillometric BP percentiles in a nationally representative sample of 14 266 randomly selected Polish children and adolescents aged 7–18 years with normal weight. When compared with the German values , the 90th SBP percentile for median height was close to the corresponding percentile in boys. In contrast, in Polish girls SBP 90th percentile values were higher. BP values in Polish were lower for DBP in both sexes.
The significant differences among the percentile values of the Kulaga and previous ones raise some nontrivial questions. What do the differences mean? Are they clinically relevant? Is this the most appropriate way to solve the definition of high BP in children and adolescents?
The most relevant factors that may contribute to the observed differences are demographics (age distribution, ethnics, weight, etc…), method of BP measurement (oscillometric vs auscultatory, number of BP readings), statistical approach and time frame. The most controversial issue concerning demographics is the suitability or not to exclude overweight and obese children when reference values are obtained. Weight is positively related to BP values in children and adolescents, then, if overweight children are still included in the normative database a resulting issue is that norms for BP will continue to increase as the level of obesity changes over time. Limitations of this approach, however, include the lack of uniform definitions of overweight and obese children and adolescents. Although the auscultatory method has been the gold standard, values obtained with oscillometric methods are necessary for the near future due to the mercury ban. When BP is measured with the two methods, large differences can be appreciated in this age group despite the use of an appropriate cuff size. Whether the source of discrepancy is due to the algorithm used in the oscillometric device or to the observer error in the conventional sphygmomanometer is, at best, speculative. Furthermore, the contribution to the different statistical approaches at the time to calculate thresholds seems to be relevant .
Another element to consider is the secular trends in BP values over time. Trends in childhood BP have few studies but are of particular interest in the light of substantial increases in the level of child obesity, the most important environmental factor of high BP in this age group. Because of the association between obesity and BP, it may be expected that levels of SBP and DBP among children would have also changed over the last few decades in parallel with changes in body mass index. This parallel association was not the case for some of the studies and in those in which an association was observed, it did not explain all the BP changes .
One intriguing question is the clinical relevance of a given threshold, which depends on the source from which it has been obtained. There are several methods to obtain ‘reference values’. The gold standard is to refer to the risk to develop cardiovascular or renal events. Nothing of the like is available in children and adolescents. The remoteness of incident cardiovascular events from BP values many years beforehand makes the relationship of BP values with events hardly feasible. In this age group, the method used is purely statistical definition because it is based on percentile distribution of the population studied and hypertension is defined as SBP and/or DBP persistently 95th percentile or more, measured on at least three separate occasions. Evidence developed in recent years, however, demonstrates that high-normal BP is not an entirely benign condition and raises the question as to whether the 95th percentile criteria for hypertension in children sufficiently captures current and subsequent cardiovascular disease risk [7–10]. Besides the relationship with left ventricular mass [11,12] and carotid intima–media thickness , the relevant clinical impact of such values is that childhood BP has been shown to track into adulthood, and children with elevated BP are more likely to become hypertensive adults, an observation emphasizing the importance of BP control in children and adolescents .
Consequently, how can we approach the definition of hypertension in children and adolescents? Facing the impossibility of having event-based studies, as has been mentioned previously, confronting BP values with the presence and the development of surrogate markers of hypertension-induced damage (heart, blood vessels and kidney) can contribute to defining more relevant thresholds. ESH guidelines in children and adolescents recommended collecting information about early organ damage so as to refine risk stratification developing thresholds and using the information to set intermediate objectives during treatment rather than using arbitrary cutoff points. The problem of pediatric hypertension is among us right now. Children are now commonly having their BP measured but clinicians need to have better tools to recognize and diagnose high-normal BP and hypertension. Despite considerable progress, there is much yet to be done in the management of high BP in children and adolescents.
Conflicts of interest
There are no conflicts of interest.
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