Suggested revision of the National High Blood Pressure Education Program blood pressure standardization for use in severely growth retarded children
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KeywordsBlood Pressure Standard Deviation Score Polynomial Regression Model Simple Regression Model Short Child
In 2007, the updated 4th report of the National High Blood Pressure Education Program was published  (http://www.nhlbi.nih.gov/health/prof/heart/hbp/hbp_ped.pdf). This report represents an international standard for the evaluation, diagnosis, and treatment of high blood pressure (BP) in the pediatric population and is based on data collected from 63,227 non-obese US children. BP measurements can be expressed as standard deviation scores (SDS) by subtracting the child’s expected blood pressure, based on age and height percentiles, from the measured blood pressure and by dividing the resulting difference by one standard deviation. To correct BP for the height z score, the authors have used fourth-degree polynomial regression models , also reported in appendix B of the report . These models, one for each gender and for both systolic and diastolic blood pressures, are very useful to generate standardized measurements. They are often used both in clinical practice and in the context of clinical trials and constitute the basis on which blood pressure tables have been generated [1, 2]. However, these models were developed on data from healthy children with expected normal heights, while children with grossly abnormal height z scores (< −6 and >6) were excluded.
In this letter we would like to emphasize the need to exercise caution when using these formulas in severely growth retarded children (i.e., height z score below −3), such as children with end-stage renal disease, of in whom approximately 20% have height z scores below −3  and who are at particularly high risk of hypertension.
To correct BP data for height z score only between −3 and +3 scores. Below and above these values, no further correction should be applied. This solution may be more prudent as no reference data are available for very short and very tall children.
To use a simpler regression model. As stated by the authors of the fourth report,  “blood pressure levels appear to have an approximately linear function of height z score for a given age-group”, which is also illustrated in Fig. 1. The relation between BP and height z scores could be recalculated using a linear or a quadratic line as shown in Fig. 1a.
In conclusion, the recently published formula for BP values correction for patients’ height z score is inappropriate for very short children. A revision is needed for their use in this particular population of children, both in the clinical setting and for research purposes.
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- 3.U.S. Renal Data System (2008) Atlas of chronic kidney disease and end-stage renal disease in the United States. National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MDGoogle Scholar