Blood pressure usually increases as children grow. Since children do not grow at the same rates, however, age alone is not enough to determine normal levels for a child’s blood pressure. Height and gender are also considered, both to avoid misdiagnosis of children who are tall for their age and to avoid missing hypertension in very short children.

It is common for people to have elevated blood pressure readings when these measurements are taken in a medical setting. Called white coat hypertension, many patients, young and old, become nervous by the surroundings, the potentially serious nature of a medical office visit or other concerns. These anxieties may cause a temporary rise in blood pressure that leads to a misleading reading. To reduce the risk of misdiagnosis, readings may be taken at several times during the office visit or again at a later date.

While any diagnosis of high blood pressure is made with the help of multiple blood pressure readings over time, additional precautions may be taken with children. Typical childhood reaction to medical tests (e.g., agitation, fear, crying) can all raise blood pressure readings significantly. Multiple testing is therefore common and home blood pressure monitoring may be advised to aid in diagnosis.  

When diagnosing high blood pressure in children, physicians compare the results of their tests against the child’s peer group, taking into account the child’s gender, age and height. Based on this, the National High Blood Pressure Education Program Working Group has developed categories to help define blood pressure. They include:

• Normal. Systolic and diastolic blood pressure are less than the 90th percentile.
  
  
• Prehypertension. Systolic and/or diastolic blood pressure are greater than or equal to the 90th percentile, but less than the 95th percentile, or if blood pressure exceeds 120/80 mmHg even if less than the 90th percentile.
  
  
• Stage 1 hypertension. Systolic and/or diastolic blood pressure between the 95th percentile and the 99th percentile.
  
  
• Stage 2 hypertension. Systolic and/or diastolic blood pressure greater than or equal to the 99th percentile.

The systolic and diastolic readings are of equal importance. If there is a disparity, the number with the higher value is used to determine high blood pressure.

The table below provides an example of the measurements physicians use to determine high blood pressure in children. The readings given are for children in the 95th height percentile (e.g., taller than 95 percent of their peers), and for the children at the older end of a given age range. The blood pressure readings given would place a child above the 90th percentile in blood pressure, which may indicate a diagnosis of prehypertension.

The table below provides highlights of the guidelines used to determine abnormally high blood pressure in children. The cut–off points listed are for general information only. This chart does not provide the detailed breakdowns, which vary by a child’s height, used by physicians when making a diagnosis. People are encouraged to speak to their physicians about individual cases. NOTE: All blood pressure measurements are in millimeters of mercury (mm Hg).

Source: Adapted from the National Heart Lung & Blood Institutes Blood Pressure Tables for Children and Adolescents

In order to be considered “normal” BOTH the upper number systolic pressure and the lower number diastolic pressure of a blood pressure reading must be below the 90th percentile for that child's age, height and gender. However, if EITHER number is above the 95th percentile, then a diagnosis of hypertension may be made. As with adults, readings higher than normal but not yet within high ranges are considered prehypertension.

The relationship between diastolic and systolic readings, as well as the numbers themselves, can be helpful in analyzing blood pressure readings. For example, kidney problems generally cause extreme highs in both diastolic and systolic blood pressures. Therefore, this cause is less likely in a prehypertensive child whose diastolic pressure is normal.