The need to identify cardiovascular risk factors, including high blood pressure (BP), not only in adults but also in children and adolescents, is now more and more frequently acknowledged [1,2]. There was a time when the routine assessment of BP, as a part of pediatric well-child care, was questioned because of the low prevalence of hypertension and of the low immediate risk this condition carries to most children. Today, however, this attitude has deeply changed. At variance from a few years ago, it is now well accepted that BP values in children represent one of the most important measurable markers of cardiovascular risk later in life . Moreover, there is an increasing awareness of the existence of a higher prevalence of essential hypertension than initially expected among children and adolescents, and the recognition that BP tracks from childhood into adulthood facilitates the identification of children at risk for the development of essential hypertension as adults .
BP is a parameter that changes on a beat-to-beat basis in response to a variety of physiological and environmental stimuli. This is an acknowledged problem for office or clinic BP measurements, which are, by definition, unable to account for the different components of BP variability over 24 h and to provide a comprehensive picture of the average BP levels typical of a given individual patient [5,6]. In spite of this, casual BP measurements have been for many years the cornerstone for the epidemiology, research and clinical management of hypertension, and have provided the basis for present knowledge of the potential risks associated with hypertension [7–9]. However, progressive awareness that a few BP measurements obtained in the office may not necessarily reflect the true BP of an individual has stimulated the implementation of additional approaches aimed at a better characterization of BP levels, with the perspective of a better stratification of risk. In particular, methods that allow the acquisition of a large number of BP measurements under normal living conditions [10,11] are also increasingly used in this young population of individuals. This is now possible through ambulatory BP monitoring techniques, as well as through the use of home self-BP monitoring. Both these approaches allow information on BP levels to be gathered from repeated measurements, obtained in daily life conditions. Such measurements, in young and physically active individuals, are likely to yield BP values different from those obtained at rest in the artificial environment of a clinic or of a doctor's office [12,13]. By applying ambulatory or home BP monitoring together with office BP readings in a given individual, four possible BP conditions can be identified: sustained or true normotension, characterized by normal levels of both office and out-of-office BP; sustained hypertension, characterized by elevation in both office and out-of-office BP; ‘white coat hypertension’ or ‘isolated office hypertension’, characterized by an elevation of office BP accompanied by normal out-of-office BP levels; and ‘masked hypertension’, defined by an elevation of out-of-office BP accompanied by normal office BP levels . Recent data from our groups, in particular, have emphasized the clinical relevance of the identification of masked hypertension in childhood, because of its reported association with hypertension-related organ damage, mainly when associated with overweight or obesity (Fig. 1).
One of the most important indications for use of ambulatory BP and/or of home BP monitoring as diagnostic tools, is indeed the identification of intraindividual differences between office and out-of-office BP measurements, but little data are available on a direct comparison between the information provided by home and by ambulatory BP monitoring when used for this aim in young individuals.
In the present issue of the Journal of Hypertension, Stergiou et al. have published an interesting study that compares the information provided by home BP measurements with that offered by 24 h ambulatory BP monitoring, in the diagnosis of sustained, white coat and masked hypertension in children and adolescents, a population in which data from home BP have been scarce up to now. The study was performed in 102 individuals from 6 to 18 years of age, including 64 boys (mean age 12.8 ± 2.9 years, range 6–18 years), who were referred to a hypertension center for elevated BP, and in whom BP values were assessed by means of clinic (two visits), home (6 days) and awake ambulatory BP measurements. It should be noted that recruitment of individuals referred to a hypertension center represents an inherent limitation of the study, leading to a selection bias when assessing the prevalence of sustained, white-coat and masked hypertension conditions, but this did not prevent a comparison between the specific information provided by different BP measuring techniques to be made. Interestingly, in this study the highest systolic BP values were observed for awake ambulatory BP, the lowest for home BP, with office systolic BP lying in-between. In contrast, diastolic BP values were similar for office and home BP, whereas awake ambulatory diastolic BP values were the highest. These between-method discrepancies resulted in differences in the diagnosis of sustained, white coat or masked hypertension in children and adolescents, as a function of the technique used for their out-of-office BP monitoring. In particular, more white coat and less masked hypertension were diagnosed when home BP was used instead of ambulatory BP monitoring to be compared with office BP readings, and vice versa. On the basis of clinic and ambulatory BP comparison, 52% of individuals were defined as sustained normotensive individuals, 20% as sustained hypertensive patients, 18% had white coat hypertension and 11% masked hypertension. Conversely, on the basis of clinic and home BP comparison, the above BP conditions were observed in 55, 15, 23 and 8% of young individuals, respectively. There was an agreement between ambulatory and home BP in the diagnosis of hypertension in 82 cases (80%). By taking ambulatory BP as the reference method for the diagnosis of sustained hypertension, the sensitivity, specificity and positive and negative predictive value of home BP were 55, 92, 74 and 82%, respectively. The corresponding figures for the diagnosis of white coat hypertension and masked hypertension were 89, 92, 70 and 98%, and 36, 96, 50 and 93%, respectively. These data suggest that the assignment of an individual to one or another BP group may differ according to the method selected for out-of-office BP measurement.
The discrepancies observed among office, home and ambulatory BP could be attributable in part to two factors. First, this young study population performed a marked degree of physical activity during the ambulatory BP monitoring period, whereas office and home BP measurements were taken when children were at rest, surrounded by a more or less relaxed environment. Second, office BP was obtained using an auscultatory method, whereas ambulatory and home BP were measured with oscillometric devices.
The oscillometric devices used for home and ambulatory BP monitoring, manufactured by Omron (Omron Healthcare, Co., Ltd, Ukyo Kyoto, Japan) and Spacelabs (Spacelabs Healthcare, Issaquah, Washington, USA), respectively, make use of different algorithms to calculate systolic and diastolic BP from the point of maximal oscillation in air-cuff pressure, which might have introduced further differences between the BP measurements obtained by these techniques.
The results of this study offer the basis for some more general considerations on BP measurement in young individuals. First, even if ambulatory BP and home BP monitoring appear to have considerable potential for use in clinical practice and research when focusing on the hypertension of children and adolescents, office BP measurements still appear to remain the recommended method for the daily management of BP in subjects of this age, until more data become available. However, increasing use of out-of-office BP is to be encouraged to better clarify the significance of white coat and masked hypertension in children and adolescents, in whom it is still uncertain. Among others, follow-up studies are necessary in order to know the persistence and the clinical significance of white coat and masked hypertension in this age group, and to evaluate the risk of developing sustained hypertension later in life. There are currently no data on the long-term follow-up of children found to have white coat hypertension upon initial assessment. In particular, the questions concerning reproducibility of this phenomenon and whether in children and adolescents it represents an innocuous finding or, conversely, it is a prelude to future permanent adult hypertension, still need to find a proper answer. On the contrary, only one follow-up study in 234 adolescents has been published in relation to masked hypertension. These data showed that 1 out of 10 individuals with masked hypertension is predisposed to the development of sustained hypertension, displaying a higher left ventricular mass index with a prevalence of left ventricular hypertrophy of 10%. Furthermore, if assessing the reproducibility and the clinical significance of the discrepancies among office, home and ambulatory BP is important in the general population, it is even more so in children and adolescents, in whom differences in growth and development rate are important determinants of BP values.
Second, more studies are also needed to define reference values for a proper clinical interpretation of home and ambulatory BP in children and adolescents. In this age group, interpretation of office BP is based on the use of population-based percentiles rather than single thresholds for hypertension diagnosis [15,16]. This is because BP in childhood and adolescence increases steadily during growth and maturation, adolescence representing a fast growth period during which body mass and BP change rapidly . For these reasons, tables reporting reference BP values specific to sex, age and/or height have been introduced for office BP in children and adolescents by the Task Force for Blood Pressure in Children , and similar indications are also available for ambulatory BP [18–20]. So far only one study  has attempted to provide reference values for normal home BP in a population of individuals with an age range from 6 to 18 years. Indeed, the need for a separate definition of reference values for different BP-measuring approaches in this age group is even stronger than in adults, given that in children and adolescents daytime ambulatory BP, home BP or office BP may differ to a larger extent, probably in relation to behavioural factors .
Finally, the increasing interest towards a more regular application of home and ambulatory BP in children and adolescents has also to face the fact that very limited data on validation of oscillometric devices for this age group have been published (see www.dableducational.org). Moreover, it is often difficult to obtain cooperation from children when planning repeated BP measurements in daily life, the ideal frequency of which is still undetermined.
In conclusion, although office BP measurement remains the recommended method for the evaluation of BP in children and adolescents, ambulatory and home BP monitoring appear to have considerable potential for use in clinical practice and hypertension research in this population, but more evidence is needed on their methodology and clinical utility. In particular, future research is needed to offer stronger normative data, and important information to help delineating more precise guidelines aimed at indicating when, and for whom, ambulatory BP and home BP monitoring would be advantageous amongst children and adolescents.
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