Understanding Blood Pressure Numbers

Systolic? Diastolic? What does it all mean?



Normal Blood Pressure

A systolic reading of less than 120 and a diastolic pressure of less than 80. If you're in this category, give yourself a congratulatory pat on the back—but don't rest on your laurels. Your lifetime risk of developing hypertension is still 90 percent. Continue to follow a healthy lifestyle to ensure that your blood pressure remains normal.


Systolic blood pressure of 120 to 139 or diastolic pressure of 80 to 89. This is a new category, introduced in May 2003 in the seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Think of it as a warning sign that you need to get your act together before it's too late. If you fall into this category, you are at increased risk of progressing to full-blown hypertension. So yes, you should be afraid. Those in the 130/80 to 139/89 mmHg range are twice as likely to develop hypertension as those with lower readings.

Stage 1 Hypertension

Systolic blood pressure of 140 to 159 mmHg or diastolic pressure of 90 to 99 mmHg. In this stage, you may require medication, although aggressive lifestyle changes (in diet and fitness) may help you avoid having to take prescription drugs.

Stage 2 Hypertension

A systolic reading of 160 mmHg or higher or a diastolic reading of 100 mmHg or higher. In this stage, you can expect to be placed on medication, as well as be counseled to make significant lifestyle adjustments.

Naturally, there are other considerations when contemplating your blood pressure readings. Here are but a few:

  • If you have diabetes or kidney disease. The American Diabetes Association and the National Kidney Foundation say you should maintain a blood pressure below 130/80 mmHg for optimal health. In other words, their threshold for taking action against high blood pressure is lower than for people without diabetes or kidney disease.
  • If you are in your late 60s or older. You may have what's called isolated systolic hypertension (ISH), in which your systolic blood pressure remains high while your diastolic pressure is normal. In the old days (pre-1991), doctors didn't even treat this condition, believing it was a normal part of aging. Now we know differently. Treating ISH with low-dose (and inexpensive) diuretic drugs reduces the incidence of stroke by 36 percent and nonfatal heart attack by 27 percent in those over 60.
  • If your diastolic and systolic numbers are unusually wide apart. Pulse pressure is the difference between systolic and diastolic blood pressure. A 1999 article in the journal Circulation asserted that it is a better predictor of overall heart disease risk than either blood pressure reading. A normal pulse pressure is 30-40 mmHg. More or less than that is considered problematic. An important note: If your systolic and diastolic pressures fall into different categories, your doctor will rate your blood pressure by the highest category. For example, 150/85 mmHg is classified as stage 1 hypertension, not prehypertension.
  • If your blood pressure measurements vary over time. As mentioned earlier, a single blood pressure reading is just a snapshot in time that reflects as much on the previous few days' diet and stresses as on your broader health. Some people's pressure increases merely because they are at the doctor's office, getting a blood pressure reading. If you and your doctor believe that better monitoring is important, consider ambulatory blood pressure monitoring, in which you wear a monitor for 24 hours. During that time, the monitor takes periodic readings, collecting them for your doctor to evaluate.

With the plethora of easy-to-use home blood pressure monitors on the market, people with high blood pressure should consider having one under their bathroom sink and should use it frequently to monitor their pressure. A good time to check your blood pressure is about an hour after you wake up. Although blood pressure is typically highest in the morning, one major study published in the journal Circulation, March 2003, found that those with highest morning "surge" (the difference between the systolic pressure's lowest value at night and the highest one during the two hours after getting out of bed) were most likely to have a stroke.

Researchers identified a "high" morning surge as at least a 55-point difference, finding that those with such a high surge were three times as likely to have a stroke as those with lower surges. For you, this means that if you have systolic values in the morning that are much higher than what you measure at other times in the day, give your doctor a call. Your blood pressure medication may need to be adjusted for better control.