Since a significant percentage of Americans suffer from high blood pressure but are unaware of the fact, it is important to recognise what is considered a normal range of blood pressure. Unfortunately, an individual's blood pressure can vary widely even without having hypertension. Blood pressure is usually highest in the morning after rising, and lowest during the night. However, activity can send normal blood pressure up. The state of the kidneys, which are part of the blood pressure control system, can cause individual variations. Even changes in body position alter the blood pressure. All these variations are normal.
The latest medical thinking assumes that a blood pressure of 120 over 80 is the midpoint of the "normal" range. High normal is a systolic reading between 130 and 139 with diastolic readings from 85 to 89. Low normal is defined as systolic readings from 99 to 90 and diastolic measuring 64 to 60. These low normal readings are usually considered fully normal only for athletes or children. The high normal readings, which were called that for many years, are now defined by some doctors and agencies as "pre-hypertension."
What is defined as a normal range of blood pressure has changed over the years. It is known that children and infants usually have much lower readings than adults. In industrialised countries, blood pressure increases with age. Systolic (the higher number) pressure usually increases at least until 80, while diastolic (the lower number) tends to increase until 55 to 60, when it levels off and at times decreases.
Patients concerned about their blood pressure may be advised by their doctor to get a home blood pressure monitor and check their readings at specified times over the course of several weeks. Single isolated readings in a doctor's office are not necessarily the best way to decide whether the individual's blood pressure is normal.
Elevated readings in special settings do not always take one out of the normal category. For example, in a doctor's office a high reading can be due to a phenomenon called "White Coat Hypertension." The patient is simply reacting to a stressful situation. Another name for this is labile blood pressure, where the pressure varies more than usual with the situation.
Some authorities feel that labile blood pressure could mean the pressure is elevated in other, more normal conditions, or that labile blood pressure may later develop into true hypertension.