Tips to measure your blood pressure correctly

To determine whether you have hypertension, a medical professional will take a blood pressure reading. How you prepare for the test, the position of your arm, and other factors can change a blood pressure reading by 10% or more. That could be enough to hide high blood pressure, start you on a drug you don't really need, or lead your doctor to incorrectly adjust your medications.

National and international guidelines offer specific instructions for measuring blood pressure. If a doctor, nurse, or medical assistant isn't doing it right, don't hesitate to ask him or her to get with the guidelines.

Here's what you can do to ensure a correct reading:

• Don't drink a caffeinated beverage or smoke during the 30 minutes before the test.

• Sit quietly for five minutes before the test begins.

• During the measurement, sit in a chair with your feet on the floor and your arm supported so your elbow is at about heart level.

• The inflatable part of the cuff should completely cover at least 80% of your upper arm, and the cuff should be placed on bare skin, not over a shirt.

• Don't talk during the measurement.

• Have your blood pressure measured twice, with a brief break in between. If the readings are different by 5 points or more, have it done a third time.

There are times to break these rules. If you sometimes feel lightheaded when getting out of bed in the morning or when you stand after sitting, you should have your blood pressure checked while seated and then while standing to see if it falls from one position to the next.

Because blood pressure varies throughout the day, your doctor will rarely diagnose hypertension on the basis of a single reading. Instead, he or she will want to confirm the measurements on at least two occasions, usually within a few weeks of one another. The exception to this rule is if you have a blood pressure reading of 180/110 mm Hg or higher. A result this high usually calls for prompt treatment.

It's also a good idea to have your blood pressure measured in both arms at least once, since the reading in one arm (usually the right) may be higher than that in the left. A 2014 study in The American Journal of Medicine of nearly 3,400 people found average arm- to-arm differences in systolic blood pressure of about 5 points. The higher number should be used to make treatment decisions.

In 2017, new guidelines from the American Heart Association, the American College of Cardiology, and nine other health organizations lowered the diagnosis of high blood pressure to 130/80 mm Hg or higher for all adults. The guidelines also redefined the various blood pressure categories to now include normal, elevated, Stage 1 hypertension, Stage 2 hypertension, and hypertensive crisis (see "Blood pressure categories").

Blood pressure categories

Blood pressure category

SYSTOLIC
(upper number)

DIASTOLIC
(lower number)

Normal

Less than 120 mm Hg

and

Less than 80 mm Hg

Elevated

120-129 mm Hg

and

Less than 80 mm Hg

High blood pressure: Stage 1 hypertension

130-139 mm Hg

or

80-89 mm Hg

High blood pressure: Stage 2 hypertension

140 mm Hg or higher

or

90 mm Hg or higher

Hypertensive crisis (consult your doctor immediately)

Higher than 180 mm Hg

and/or

Higher than 120 mm Hg

Source: American Heart Association and American Stroke Association.

For more on getting your blood pressure under control, buy Controlling Your Blood Pressure, a Special Health Report from Harvard Medical School.

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