Medical Procedures

The Right Way to Read Blood Pressure

Blood pressure can be a crucial indicator of health, but results can sometimes be misleading. Here, from the Harvard newsletter Health Beat, is how to take your blood pressure correctly.

First of all, the Harvard experts say, don’t underestimate the importance of getting a good reading; how you prepare for the test and even the position of your arm can distort the result by 10 percent or more. And that, the experts say, can hide the fact that you have hypertension, or cause your doctor to adjust the medications you’re taking, or even get you started on a medication you don’t need.

But you can get an accurate reading if a health-care practitioner follows national guidelines, the Harvard letter says.

Here’s what they are:

Don’t drink a caffeinated beverage or smoke for 30 minutes before the test.

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

Sit quietly for five minutes before beginning the test.

During the test, you should be sitting in a chair with your feet on the floor and your arm supported, the Harvard letter says, “so your elbow is at about heart level.” (However, the letter says, if you occasionally feel lightheaded when getting out of bed or standing after sitting, your blood pressure should be checked while seated and then while standing to see if it drops between those two positions.)

Make sure that the inflatable part of the cuff covers at least 80 percent of your arm. The cuff should be on your bare arm, not over a shirt.

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 test.

Ask for your blood pressure to be measured twice, with a brief break. If the readings differ by 5 points of more, the Harvard letter says, have your blood pressure done a third time.

You should also have blood pressure measured in both arms at least once. The reading in the right arm, the Harvard letter says, may be higher – usually a difference of about 5 points in the systolic number, according to a 2014 study cited in the Harvard letter. The higher number, the Harvard experts say, should determine “treatment decisions.”

Your health care practitioner won’t usually diagnosis hypertension based on one reading. A conclusion is usual based on at least two readings within a few weeks. If, however, you have a reading of 180/110, that calls for quick treatment.

The Harvard letter gives some basic guidelines for numbers and monitoring:

Readings between 160/100 and 179/109 – recheck within two weeks.

Between 140/90 and 159/99 – recheck within four weeks.

Between 120/80 and 139/89 (prehypertension) – should be rechecked within four to six months.

Less than 120/80 (normal) should be recheck annually.

But, the Harvard letter emphasizes, your doctor may not follow these numbers exactly if there are signs of sharply lower blood pressure or damage to vital organs.