DIFFERENTIAL CLASSIFICATION OF BLOOD-PRESSURE BY 4TH AND 5TH KOROTKOFF PHASES IN SCHOOL-AGED GIRLS - THE NATIONAL-HEART-LUNG-AND-BLOOD-INSTITUTE GROWTH AND HEALTH STUDY

The use of the onset of the fourth (K4) or fifth (K5) Korotkoff phase to determine diastolic blood pressure in children has been controversi al; most recently, the Second Task Force recommended the use of K4 for children up to age 13 years and K5 for children age 13 and above. We performed a cross-sectional analysis of 1,155 nine-year-old (53% white and 47% black) and 1,224 ten-year-old girls (45% white and 55% black) in the National Heart, Lung, and Blood Institute Growth and Health St udy (NGHS). The mean blood pressures for the first fourth, and fifth K orotkoff phases were 100.1 (+/-8.9) mm Hg, 66.6 (+/-9.8) mm Hg, and 56 .8 (+/-11.8) mm Hg for nine-year-olds and 102.8 (+/-9.0) mm Hg, 68.1 ( +/-10.1) mm Hg, and 58.1 (+/-11.9) mm Hg for ten-year-olds. The mean d ifference between K4 and K5 was 9.9 (+/-6.4) mm Hg. The correlation be tween K1 and K4 was 0.45, between K1 and K5 was 0.34, and between K4 a nd K5 was 0.84. Elevation of blood pressure was defined at or above th e 95th percentile based on the NGHS distribution for K1, K4, or K5; th e relative risk of having an elevated K1 was 10.1 if K4 was elevated a nd 5.9 if K5 was elevated. Of the 159 subjects potentially classified with elevated diastolic pressure, 95 subjects (60%) would be classifie d differently depending on whether K4 or K5 was used to define elevate d diastolic blood pressure. The choice of the onset of the fourth or f ifth Korotkoff phase for determining diastolic blood pressure in child ren may have important implications for which individuals are classifi ed as having hypertension.