Combining annual blood pressure measurements in childhood to improve prediction of young adult blood pressure

Tracking correlations of blood pressure (BP) have been reported between lev els measured in a single year during both childhood and adulthood. Because of the variability of BP, these correlations increase with the number of vi sits and measurements per visit in each year. It remains unclear, however, whether such correlations would improve further by combining BP data collec ted over several years. From 1978-1981, BP was measured annually in a cohor t of 339 children in East Boston, MA, at four visits one week apart with th ree measurements per visit. Of this cohort, then aged 18-26 years, 316 were re-examined in 1989-1990 at three visits one week apart with three measure s per visit. Tracking correlations were estimated from levels measured in a single year as well as means averaged over several years in childhood, adj usting for age, year of measurement, as well as smoking, alcohol and oral c ontraceptive use. Multivariate models were fit to estimate tracking correla tions from childhood to young adulthood adjusting for within-person variabi lity. Using a single year in childhood, these were 0.49 in boys and 0.59 in girls for systolic BP and 0.39 and 0.48 for diastolic BP (all p < 0.001). Using the long-term average in childhood and adjusting for variability acro ss years, these values were 0.55 in boys and 0.66 in girls for systolic BP and 0.47 and 0.57 for diastolic BP (all p < 0.001). We observed concomitant increases in the predictive value of childhood BP for young adult BP. Thes e results suggest that averaging BP over at least two years during childhoo d increases tracking correlations and improves the prediction of adult valu es from childhood levels. Copyright (C) 2000 John Wiley & Sons, Ltd.