A blood pressure reading with a systolic measurement under 120 and a diastolic measurement below 80 is considered normal, and readings outside this range are considered abnormal. Normal blood pressure readings may be lower in children and teenagers, according to Mayo Clinic.
Blood pressure with a systolic reading between 120 and 139 or with a diastolic reading between 80 and 89 is considered prehypertension, states MedlinePlus. There are two stages of high blood pressure: stage 1 and stage 2. Stage 1 has a systolic reading between 140 and 159 or a diastolic number between 90 and 99. Stage 2 hypertension is identified when the systolic reading is 160 or higher or the diastolic number is 100 or higher, states the National Heart, Lung and Blood Institute.
Blood pressure can also be too low. Symptoms of low blood pressure include a reading with a systolic pressure under 120 and a diastolic pressure less than 80, dizziness, fainting, dehydration, and blurred vision, reports the American Heart Association.