Is your home blood pressure monitor accurate?

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An inexpensive, easy-to-use blood pressure monitor that you use at home is a powerful tool to protect your health. It can help you see if your blood pressure is under control and how it responds to new medications or exercise. It may even provide a more realistic picture of your blood pressure than measurements taken in a doctor's office, which can vary for many reasons. But home monitoring can have problems, too — namely, the equipment.

In a letter published May 2, 2023, in JAMA, an international team of researchers reported findings indicating that the vast majority of top-selling blood pressure monitors sold on a popular website are not validated for accuracy. And using a nonvalidated device might threaten your health.

The researchers identified the top-selling home blood pressure monitors available on Amazon.com in 2020 in 10 countries, including the United States. Then they checked to see how many of the devices were validated for accuracy.

Most of the devices — 79% of those with an upper arm cuff and 83% of those with a wrist cuff — were not validated. Most of the nonvalidated arm cuff devices were sold in India or Australia. Most of the nonvalidated wrist devices were sold in the United States or Mexico. Other studies also have suggested that 85% to 94% of all available blood pressure devices are not validated. This poses a risk.

Using a nonvalidated device to measure your blood pressure means there's no way to know if the information it provides is correct. And relying on inaccurate measurements could then affect decisions you and your doctor make about treatment. For example: "Inaccurate measurements that appear too high or low might warrant trips to the doctor's office — unnecessarily. The measurements might also lead your doctor to start you on a blood pressure drug or adjust your current blood pressure medications, even though they might not need to be changed. Taking too much or too little of the drugs might harm your health," says Dr. Christopher Cannon, a cardiologist and editor in chief of the Harvard Heart Letter.

Why are so many blood pressure monitors nonvalidated? It's hard to standardize and enforce rules for manufacturers based in different countries around the world. There's no global institution that does this.

Instead, we have medical organizations in varying countries or international groups that set validation guidelines for clinical accuracy. It's then up to manufacturers to pay independent investigators to test their devices and make sure they follow at least one set of guidelines.

But device makers aren't always required to have their products validated. In the United States, for example, manufacturers need to prove to the FDA only that a blood pressure monitor is safe to get it cleared for marketing. By "safe," the law means that the machine doesn't injure you when you take your blood pressure. But a machine that provides you with an inaccurate reading is unsafe in another way: it can lead to inadequate or excessive treatment.

Fortunately, reliable organizations have developed lists of blood pressure monitors that have demonstrated clinical accuracy based on a formalized set of criteria. The lists enable you to look up blood pressure monitors by brand name, device name, model number, or other details.

For blood pressure monitors available in the United States, with validation criteria set by the American Medical Association and other U.S. groups and experts, consult the U.S. Blood Pressure Validated Device Listing, or VDL (https://validatebp.org).

For blood pressure monitors that meet validation criteria set by organizations outside the United States, check out STRIDE BP (https://stridebp.org/bp-monitors).

When choosing a blood pressure monitor, remember to check the cuff size to see if it fits you properly. It should be wide enough to cover about 80% of your upper arm, from your elbow to your armpit, and fit comfortably. And it should be long enough, based on the circumference of the middle of your upper arm at the biceps, in centimeters (cm). Cuff sizes are

If possible, measure your arm before shopping for a blood pressure monitor.

If you have a blood pressure monitor, look it up on one of the device lists to see if it's validated for accuracy. If it doesn't show up, it's probably not validated. But there's still a chance it's accurate.

"To find out, bring the monitor to your next doctor appointment and ask a nurse to take one measurement with your monitor and another with a monitor there in the office," Dr. Cannon says. "If your monitor isn't accurate, it's time to invest in a new one."

You don't need a blood pressure monitor that costs more than $50 to $100. Just make sure it has several important features, including a large, easy-to-read display and a cuff that wraps around your upper arm (see "Cuff size matters") and inflates automatically. (Finger or wrist monitors are not considered reliable.)

The blood pressure cuff needs to fit well, since cuffs that are too small will give falsely elevated readings. "I have a patient who was getting very high readings that were different in both arms," Dr. Cannon says. "He brought his blood pressure monitor in, and sure enough, the reading on his home device was much higher than what our monitor in the clinic showed. His biceps were huge and the standard cuff size was too small for him."

It's also handy if the blood pressure monitor has a battery life indicator or, even better, if it can plug into an electrical outlet (so you don't have to worry about replacing batteries).

The monitor should be approved by the FDA and validated by the VDL or STRIDE BP.

Follow these steps to measure your blood pressure at home:

When you first start measuring blood pressure at home, take it early in the morning and again in the evening, every day for a week. If most readings fall within the goals recommended by your doctor, you can check your blood pressure two or three times per week, and eventually once a month.

If you notice changes, report them to your doctor's office.

Heidi Godman , Executive Editor, Harvard Health Letter

Anthony L. Komaroff, MD , Editor in Chief, Harvard Health Letter

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