A longitudinal study of blood pressure in Spanish schoolchildren. Working Group of Cardiovascular Risk Factors in Childhood and Adolescence.

Blood pressure (BP) values and the phenomenon of tracking were evaluated in a group of 481 schoolchildren over a nine year period starting at age 6 years. BP values were obtained yearly by taking the mean of two measurements at one visit, measurements were taken by only two observers during the study. For both systolic and diastolic BP, correlation coefficients between year 9 and previous measurements increased as the year of examination approached year 9, and ranged from 0.79 to 0.81 for systolic BP, and from 0.52 to 0.55 for diastolic BP. For children in the upper quartile of systolic BP at any previous examination, more than 70% remained in the upper quartile at the year 9 examination. More than 90% of children who were not in the upper quartile of systolic BP at any previous examination remained in non-upper quartiles at year 9. This novel longitudinal study of BP in a cohort of Spanish schoolchildren suggests that the degree of tracking of BP during childhood years could be higher than described previously.