Unlike high blood pressure, low blood pressure is defined primarily by signs and symptoms of low blood flow and not by a specific blood pressure number. Some individuals routinely may have blood pressure numbers of 90/50 with no symptoms and therefore do not have low blood pressure. However, others who normally have higher blood pressures may develop symptoms of low blood pressure if their blood pressure drops to 100/60.
Blood pressure readings fall into four general categories, ranging from normal to stage 2 high blood pressure (hypertension). The level of your blood pressure determines what kind of treatment you may need. To get an accurate blood pressure measurement, your doctor should evaluate your readings based on the average of two or more blood pressure readings at three or more office visits.

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Blood pressure is the force of your blood pushing against the walls of your arteries. Each time your heart beats, it pumps out blood into the arteries. Your blood pressure is highest when your heart beats, pumping the blood. This is called systolic pressure. When your heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure. Your blood pressure reading uses these two numbers. Usually they're written one above or before the other, such as 120/80. If your blood pressure reading is 90/60 or lower, you have low blood pressure.
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