Hypertension in children is frequently undiagnosed. Normal blood pressure is currently defined as a function of two continuous variables, age and height for each gender. Applying the current cutoff values to assess a child's blood pressure is time consuming. To separate the independent effect of age from that of height on blood pressure, we conducted a multiple group matched study to investigate if blood pressure levels in children with a given height distribution vary with age. An equal number of 2539 Chinese children from each of the four age groups (7, 8, 9 and 10 years) were individually matched by height, sex and geographic region. We used the matching technique to force the four age groups to have an identical height distribution. Systolic and diastolic blood pressures significantly increased with increasing age before matching. After matching, four groups had strikingly similar levels of blood pressures, and the differences among four groups were small and not statistically significant. Once height is taken into consideration, age has little impact on blood pressure. Our findings, if confirmed in children of other ages, suggest that blood pressure percentile charts can be considerably simplified by establishing normal percentiles according to height alone for each gender
