Blood pressure (BP) increases with age, like height and weight. Your pediatrician or school nurse compares your child's BP with others of similar age, gender and height on a chart to determine if your child's BP is significantly higher than normal. We describe this relationship in terms of percentiles. The 50th percentile means that 50% of children of the same age, gender and height have blood pressure below the value in the table. 90th percentile means that 90% have blood pressures below that value, similarly for 95th and 99th percentile. If a "screening" BP measurement (done for surveillance, not because the child has any complaints) demonstrates a higher than normal reading, this may indicate a situation which needs further diagnostic testing or treatment. As kidney conditions are frequently associated with hypertension, your child has been referred to a children's kidney specialist (pediatric nephrologist) for evaluation.
The 2 common explanations for high BP readings, which are not related to kidney conditions, are:
1. Obesity
This increasingly common condition in children and teenagers can be quantitated by calculation of "body mass index," and compared to other children and teenagers of similar age. Your child's BMI is ______, at the ______percentile for age. If obesity is the most likely reasons for hypertension, every effort should be made to have the child lose weight, with continued monitoring of BP to be certain that it declines with weight loss.
2. "White Coat" Hypertension
That is, high BP only in the doctor's office. This is why we frequently advise home BP measurements; if BPs are normal at home, you can be reassured. If BPs at home are high, further testing to determine the reason for hypertension should be undertaken.
If neither of these two conditions is the cause of hypertension, testing for possible causes of hypertension is the next step. This is different from adult hypertension, in which more than 90% of hypertension is thought to be genetic/familial or related to obesity (this is often the case in children and teenagers as well). Therefore, most adults do not undergo any testing to try and determine the cause of this condition. They are usually advised to lose weight, exercise, and take medication. However, in the pediatric age group the younger the child and the higher the BP, the greater the likelihood of finding an underlying cause which can be treated. Therefore, we advise that children (and less so teenagers) undergo testing.
The kidney is the most likely organ to cause hypertension, thus the referral to the pediatric nephrologist (kidney specialist.) The urine is examined for abnormalities. Sometimes protein and/or red blood cells in the urine indicate kidney disease (nephritis) and, after appropriate blood tests, a biopsy of the kidney tissue to make an accurate diagnosis (and treatment) will be recommended.
Other possible causes of hypertension involve the urinary drainage system, such as partial blockage to the flow of urine. Kidney damage from urinary infections can cause hypertension. There may be abnormalities in the size or shape of the kidneys or cysts in the kidneys. All of these conditions can be evaluated by kidney ultrasound (sonogram) and/or bladder X-ray and/or radioactivity "scan." If any of them are detected, the reason for hypertension will have been found and specific treatment undertaken. Lastly, hypertension can be caused by reduced blood flow to one or both kidneys; this must be diagnosed by a dye injection test.
A non-kidney condition of the adrenal glands (which sit on top of the kidneys) can cause hypertension as well. They can make a hormone which can increase BP. This can be diagnosed by collecting a 24hour urine for hormone measurement. Specific treatment of this disorder will cure hypertension.
All tests need not be done in every patient. Those that are youngest with the highest BP are most likely to need the most thorough evaluation. Sometimes the initial testing is unrevealing but over time new findings appear, and a specific diagnosis can be made.
Until a specific cause for hypertension can be found and treated, drug therapy is the key to restoring BP back to normal, and home BP monitoring (frequent recorded measurements) is essential to allow proper regulation of drug treatment. The damage that hypertension does to all organs (we can evaluate the stress that hypertension puts on the heart by a special sonogram, an echocardiogram) is always worse than the potential "side-effects" of BP drugs.
