High blood pressure in children goes undiagnosed about 25 percent of the time, according to a study in the Aug. 22-29 issue of the Journal of the American Medical Association.

Hypertension affects between 2 percent and 5 percent of children and is becoming increasingly prevalent due to the pediatric obesity epidemic, according to background information provided in the article.

Dr. Matthew L. Hansen, of Case Western Reserve University, Cleveland, and colleagues conducted a study to determine the frequency of undiagnosed hypertension and pre-hypertension in 3- to 18-year-old children.

The study included 14,187 children and adolescents who were observed in outpatient clinics at least three times between June 1999 and September 2006.

Of the children who had the condition, only one in four had been previously diagnosed.

The researchers found that the criteria for high blood pressure were met by 507 children or 3.6 percent of those involved in the study. But only 131 or 26 percent of them had been diagnosed with hypertension or elevated blood pressure, according to documented electronic medical records.

The study also showed that 485 children, 3.4 percent, met the criteria for pre-hypertension. Of these, 55 or 11 percent had been diagnosed with the condition, according to electronic medical records.

Diagnosis of hypertension in children is complicated because normal and abnormal blood pressure values vary with age, sex, and height, according to the article.

“Identification of elevated blood pressure in children meeting pre-hypertension or hypertension criteria is important because of the increasing prevalence of pediatric weight problems and because secondary hypertension is more common in children than adults, requiring identification and appropriate work-up," the authors wrote in their study.

The longer high blood pressure goes undiagnosed, the higher the risk of organ damage, according to researchers. They added that the problem could be corrected by developing an electronic record-keeping model that would identify children who may have high blood pressure or pre-hypertension.