TUESDAY, Jan. 29 (HealthDay News) -- The number of U.S. kids with full-blown high blood pressure could be lower than previously thought, if new research findings are on the mark.

In a study of nearly 200,000 children aged 3 to 17 years, researchers found that only 0.3 percent met the standard for high blood pressure -- elevated readings at three consecutive doctor visits.

That stands in contrast to past studies, which have suggested that anywhere from 0.8 to 4.5 percent of American kids have high blood pressure.

But experts say the "correct" rate among U.S. kids is still unknown. And even if blood pressure is lower than earlier estimates, children should still have their blood pressure measured at routine checkups, said Dr. Stephen Daniels, an expert in pediatric high blood pressure who was not involved in the new study.

The American Academy of Pediatrics and the U.S. National Heart, Lung, and Blood Institute both recommend that kids have yearly screenings for high blood pressure, starting at age 3.

"I don't think that should change," said Daniels, the chief pediatrician at Children's Hospital Colorado and head of pediatrics at the University of Colorado School of Medicine in Aurora. "I wouldn't want parents to get the message that their child doesn't need to have their blood pressure measured."

As for why the new figure is lower than past estimates, it's probably due to how the study was done, according to lead researcher Dr. Joan Lo, a research scientist with Kaiser Permanente Northern California in Oakland.

The children in her study were from three different U.S. states, and all were visiting the doctor for routine "well-child" visits. Past studies have mainly been done in schools, in a single city or region. And some of those studies were run in urban areas, with a high proportion of black and obese kids -- both of whom are at increased risk of elevated blood pressure, Daniels noted.

Still, the true rate of high blood pressure among U.S. children remains unclear, according to Daniels.

"This new study is narrow in its own way," he said, noting that the kids involved had health insurance and got routine check-ups. The group was racially diverse, but Daniels said they may have been better off -- financially and health-wise -- than a random sample of U.S. kids would be.

The findings, which appear in the February issue of the journal Pediatrics, are based on 199,513 children and teens enrolled in three large health plans.

Almost 11,000 of those kids had an elevated blood pressure reading at their first doctor visit during the study period. But after repeat tests at their next two visits, less than 4 percent of them were ultimately diagnosed with high blood pressure.

All in all, just 0.3 percent of the whole study group had confirmed high blood pressure, the researchers found.

Both Lo and Daniels said the findings underscore the importance of doing repeat measurements to confirm that a child actually has high blood pressure, and not just a temporary spike.

To nail down the true prevalence of high blood pressure, Daniels said researchers need to follow a nationally representative sample of children who have three consecutive blood pressure readings taken over time.

But whatever the true rate is, no one is calling for a change in children's routine care.

High blood pressure may not be highly common in children -- which is "good news," Daniels said. But kids with high blood pressure often become adults with the condition. If not treated properly, high blood pressure can lead to coronary heart disease, heart failure, stroke, kidney failure and other health problems.

"Blood pressure tracks from childhood to adulthood," Lo said. "So diagnosing hypertension in a child suggests it will also be present in adulthood, although this is not 100 percent predictable."

High blood pressure is diagnosed differently in children than in adults. There is no cut-off number, which in adults is a reading of 140/90 mm Hg or higher. Children are diagnosed with the condition if they have three consecutive readings that are at or above the 95th percentile for their age, sex and height.

Treatment depends on the cause, if it's known. If blood pressure is very high, Daniels noted, it is likely due to an underlying condition, like kidney disease. Otherwise, a child's numbers can often be reined in with a healthy diet, exercise and, if needed, weight loss.

More information

Learn more about high blood pressure in children from the American Heart Association.