prehypertension, also known as high normal blood pressure and borderline hypertensive (bh), is an american medical classification for cases where a person's blood pressure is elevated above normal, but not to the level considered hypertension (high blood pressure). prehypertension is blood pressure readings with a systolic pressure from 120 to 139 mm hg or a diastolic pressure from 80 to 89 mm hg. readings greater than or equal to 140/90 mm hg are considered hypertension. classification of blood pressure is based upon two or more readings at two or more separate occasions separated by at least one week. the seventh report of the joint national committee (jnc 7) proposed the new labeling for elevated blood pressure values below 140/90 to more accurately communicate the tendency of blood pressure to rise with age.