Cuff Size Affects Blood Pressure Accuracy

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Harvard Medical School
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Cuff Size Affects Blood Pressure Accuracy

News Review from Harvard Medical School

June 25, 2014

News Review From Harvard Medical School -- Cuff Size Affects Blood Pressure Accuracy

Taking your blood pressure can help diagnose a problem that could increase your risk of stroke and heart attack. But if you take the reading yourself at the drug store or the mall, you might not get an accurate result, U.S. officials warn. That's because the cuff might be the wrong size for you. Doctors can choose from many cuff sizes to get an accurate reading. But many public blood pressure machines have only one cuff. If the cuff is too small, the blood pressure reading may be too high, the Food and Drug Administration (FDA) said. If it's too big for you, the reading may be too low. Or maybe the machine won't work at all. It may help to know the size of your upper arm so you can see if the kiosk's cuff is the right size for you. The FDA said it's important to remember that a diagnosis of high blood pressure is not based on just one reading. HealthDay News wrote about the FDA statement.


By Howard LeWine, M.D.
Harvard Medical School


What Is the Doctor's Reaction?

Any chance you get to measure your blood pressure for free, do it. That includes using a machine in a kiosk. Many pharmacies have them available.

As the Food and Drug Administration warns, the reading may not be completely accurate for some people. But for most, the reading from a kiosk blood pressure machine will be accurate and valuable.

When readings are inaccurate, it's not because the machine is faulty. That happens rarely. The problem is almost always the cuff size. The cuff is probably too big or too small for your arm. And you can't change the size of the cuff in the kiosk machines.

If your arm is thick and barely fits, the blood pressure that shows on the machine may be higher than your real blood pressure. Don't be alarmed. Just arrange to get it checked with the right-size cuff. If you can, have it done by a health professional.

The greater concern is for people with thin arms and a cuff that is too large for them. You probably can tell the cuff is too big for you if it takes a very long time for the cuff to inflate and compress your arm. Or you may not feel as much pressure on your arm as you usually do when getting your blood pressure checked.

If the cuff is too big for your arm, you may not get any reading. Or it could show a reading that is falsely normal when you actually have high blood pressure (hypertension). Or the reading may appear so low that you get worried. Again, the solution is having it done with the right-size cuff.

The right-size cuff covers 80% of the upper half of your arm. Some blood pressure devices are designed to cover the lower half. The same 80% rule applies.

Also, to get the most accurate reading, try to have the cuff touching bare skin. That may not be possible in a public kiosk. At least take off any outer layer of clothing, such as a sweater.


What Changes Can I Make Now?

The best way to track your blood pressure is with a home device. Before purchasing it, make sure the cuff is the right size for you.

There are dozens of different home blood pressure monitors on the market. For best accuracy and ease of use, buy one with a cuff for the upper arm that automatically inflates and that automatically records the pressure. Models that store readings for a week or two can simplify record keeping.

The American Heart Association recommends not using wrist or finger home blood pressure monitors. They are not as accurate.

When you first start to check your blood pressure at home, do it twice a day for a week. Measure it early in the morning, shortly after you wake up, and again in the evening. If you take blood pressure pills, check your pressure just before you take them.

Each time you take a reading:

  • Avoid caffeinated or alcoholic beverages, and don't smoke, during the 30 minutes before the test.
  • Sit quietly for five minutes with your back supported and feet on the floor.
  • When making the measurement, support your arm so your elbow is at the level of your heart.
  • Push your sleeve out of the way and wrap the cuff over bare skin. Measure your blood pressure according to the machine's instructions. Leave the deflated cuff in place, wait a minute, then take a second reading. If the readings are close, average them. If not, repeat again and average the three readings.
  • Don't panic if a reading is high. Relax for a few minutes and try again.
  • Keep a record of your blood pressure readings and the time of day they are made.

Take your new monitor with you the next time your visit your doctor's office, along with the record of your readings. The nurse or doctor can check that your machine is accurate and you are doing it right.


What Can I Expect Looking to the Future?

Similar to most home electronic devices, the quality and cost of home blood pressure monitors will continue to be reasonable. It's a great investment.

The only way to know if your blood pressure is normal is to check it. Keeping your pressure in the normal range is best way to avoid a stroke and help prevent a heart attack, heart failure and early death.

Last updated June 25, 2014

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