What Is the Meaning of the Bottom Number on a Blood Pressure Reading?

Blood pressure readings are expressed as a ratio. The top number is your systolic reading and the bottom is your diastolic reading. Both numbers play a role, individually and collectively, in the diagnosis of hypertension, commonly referred to as high blood pressure.


The bottom or diastolic reading, according to the AHA, "measures the pressure in the arteries between heartbeats." This number is lower than the top number, which measures pressure during heart beats.


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The bottom number in your blood pressure reading carries more significance prior to age 50. According to the National Heart, Lung and Blood Institute (NHLBI), the diastolic reading is "an important hypertension number," especially for younger people."The higher the diastolic blood pressure the greater the risk for heart attacks, strokes and kidney failure," reports NHLBI.

Normal Reading

Although blood pressure readings may fluctuate in reaction to stress, exercise and even sleep, a normal blood pressure reading should be less than 120/80 millimeters of mercury in adults 20 or over, reports AHA. If your bottom number is between 80 and 89, your physician may want to monitor your blood pressure to determine whether you need to be treated for hypertension.


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A bottom number reading 110 or higher indicates the need for emergency medical attention. A diastolic reading this high points to a possible hypertensive crisis which could permanently damage blood vessels and organs.

Time Frame

As you age, your diastolic reading will go down while the systolic reading increases. The top number is a more reliable indicator of the risk for cardiovascular disease in people over 50, according to the American Heart Association (AHA).