A silent epidemic of hypertension -- commonly known as high blood pressure -- may be affecting the long-term health of as many as 1.5 million American children, according to a new study released Tuesday.

The research, which is slated to appear in the upcoming issue of the Journal of the American Medical Association, looked at existing medical records of more than 14,000 children aged 3 to 18.

Researchers found that while 507 of these children and adolescents had high blood pressure, such a diagnosis had only been made in 131 of them -- suggesting that nearly three out of four cases of hypertension went undiagnosed.

Such a percentage could have big implications if they are reflected in the general population as researchers believe.

"There are approximately 2 million children in the country aged 3 to 18 who have high blood pressure, or hypertension," said lead study author Dr. David Kaelber of the Boston Children's Hospital.

Extrapolating from the study's findings, he said, only about 500,000 of these cases will be detected.

"This means that there are 1.5 million of these children that neither they, nor their parents, nor their clinicians know they have high blood pressure," Kaelber said.

Doctors not affiliated with the study said the research underscores a significant problem.

"I really think this article emphasizes the importance of doing blood pressure monitoring in children," said Dr. Tom Edwards, a pediatric cardiologist at the Cleveland Clinic. "There seems to be a significant difference between what we think the incidence of hypertension is and its correct incidence."

And if left unchecked, the problem could get worse.

"The epidemic of childhood obesity has made hypertension much more common," said Dr. Goutham Rao, clinical director of the Weight Management and Wellness Center at the Children's Hospital of Pittsburgh.

"Roughly 30 percent of overweight and obese children are hypertensive," Rao said. "As more and more children become obese, hypertension will become an increasingly common problem."

An Elusive Diagnosis

But why are pediatricians missing so many cases of high blood pressure?

As any child who has been to the doctor's office can attest, a blood pressure check is a routine part of any pediatric examination. However, the recent study shows that the data obtained through these checks is not always used in the best way possible to determine whether or not a child has high blood pressure.

This is due in part to the fact that "normal" blood pressure ranges for children vary greatly according to height, age and sex of the child -- far too many values for doctors to know by heart.

"The American Academy of Pediatrics has released guidelines for the detection and treatment of hypertension, but these are cumbersome to use," Rao said. "Doctors need easy-to-use tools to detect elevation of blood pressure."

"Even as a board-certified pediatric physician I don't know all of these values," Kaelber added. "There are literally hundreds of them."

Moreover, even if the doctor notes an abnormally high blood pressure reading at a single checkup, it takes three of these high readings on separate doctor visits to make a diagnosis of pediatric hypertension.

Doctors say an increased reliance on computerized records could be part of the solution to this problem, as electronic databases may offer a much easier and more reliable way to keep track of pediatric patients from visit to visit.

"The whole idea is that as more and more of this information is put into an electronic format, the computer will allow us to process this information in ways that we have not before," Kaelber said.

Rao agreed. "For example, in electronic health records, if blood pressure is elevated above normal ... the computerized system could send an alert to the physician."

Hypertension? Not My Child

But while computerized systems may go a long way in making sense of diagnostic data, preconceived notions about the onset of high blood pressure could stymie efforts to detect more cases of pediatric hypertension.

"Both among parents -- and unfortunately, among pediatricians -- the idea that a child could have a chronic disease in terms of high blood pressure is hard to believe," Kaelber said. "Part of that is because a child is not going to come into the doctor's office having a heart attack, stroke or kidney problems due to high blood pressure.

"In that sense, high blood pressure is very much a silent disease in children."

Unfortunately, if it is undetected in childhood, hypertension may remain silent for decades. Kaelber said high blood pressure problems missed in childhood are unlikely to be detected in the patient's 20s and early 30s -- a time during which most people assume they are in good shape and subsequently skimp on doctor visits.

"Our concern is that there is probably a cohort of people who are newly diagnosed with high blood pressure in their 40s and 50s who have actually had it for decades," he said. By this time, the condition may have already caused significant damage to the heart, the kidneys and other organs.

But there is another reason that detecting hypertension early is important; it may be a signal for other underlying and serious health conditions.

"Some children have high blood pressure secondary to an often correctable disease -- for example, kidney disease, such as renal vascular stenosis," Rao said. "Missing high blood pressure means missing such secondary causes."

What Parents Should Do

While parents may be shocked upon learning their child has high blood pressure, catching the condition early means that they can also get a head start in treating the problem.

If a child is found to have high blood pressure, a pediatrician will likely recommend three to six months of medicine-free interventions -- increased exercise and dietary changes that may cut out excess calories and salt.

"The first line of treatment for hypertension is basic: weight loss, salt restriction, and plenty of exercise," Rao said.

Edwards agreed. "As we know, obesity seems to be one of the big factors correlated with hypertension," he said. "This needs to be very aggressively treated."

After lifestyle modifications, if the child has not made significant progress, treatment may shift to medications.

Kaelber suggests that parents would also do well to be on guard against high blood pressure during routine checkups.

"Ideally, this raises awareness among parents that blood pressure is an issue among children," he said.

"And it is also a nice, gentle reminder to pediatricians that if they haven't looked at a child's blood pressure, it might be a good idea."