Blood pressure testing is often best done at home

But measuring your blood pressure accurately can be tricky. In fact, when you get it taken in a doctor’s office, there’s a good chance those numbers won’t reflect your real blood pressure on an ordinary day. Raj Padwal, a professor of medicine at the University of Alberta in Canada who runs a specialty hypertension clinic, says that he generally doesn’t ask for in-clinic blood pressure readings for his patients “because 50 percent of the time they’re inaccurate.”

There are a few reasons that readings taken in a doctor’s office can be misleading. But the good news is that there’s an easy and relatively inexpensive way to get an accurate picture of your blood pressure from the comfort of your own home.

The problem with doctor’s office blood pressure checks

Blood pressure is exquisitely sensitive, changing from moment to moment. It’s “affected by emotional status, mental health, physical activity, ambient temperature, medications, whether you ate, whether you slept well, and on and on,” Padwal says.

This vital sign is measured with two numbers: systolic pressure, the top number, which represents the pressure on your arteries as your heart contracts; and diastolic pressure, the bottom number, representing the pressure on your arteries when your heart is at rest.

Getting an accurate blood pressure reading requires following a highly specific procedure that includes keeping your feet flat on the floor, your back against a sturdy chair and your arm on a flat surface. Also, the cuff should be level with your heart and placed directly on your skin (not over your shirt) and you should empty your bladder and sit quietly for several minutes before taking the reading. But many of these requirements aren’t consistently met in a doctor’s office, where staff may be too rushed to put you in the right position.

Plus, doctors’ offices can have equipment problems. You might assume that the BP monitors there are more accurate than at-home monitors, but that’s often not the case. Analog devices that use a cuff and pressure gauge need calibration every few months, but this rarely happens, says Jordana Cohen, an associate professor of medicine and epidemiology at the University of Pennsylvania Perelman School of Medicine. Digital BP monitors, also used in medical settings, are more reliable. But only a fraction of them have been independently verified for accuracy, a process called validation. Also, your doctor’s office may not have the right cuff size for your arm, and a too-big or too-small cuff can result in an inaccurate reading.

Some people also experience what’s called white-coat hypertension, where their blood pressure rises in a doctor’s office, possibly due to the stress of a medical visit. Others have masked hypertension, in which their blood pressure falls to a lower level in a doctor’s office, possibly because those with a lot of stress in their daily lives feel calmer at a doctor’s office. The true prevalence of these conditions isn’t clear, but it’s thought that 15 to 30 percent of people have white-coat hypertension, and about 32 percent of those with normal in-office BP readings have masked hypertension.

All of this may explain why your blood pressure readings at a doctor’s office can vary so much. A 2023 study that evaluated data on more than half a million people found that between two consecutive doctor’s visits, a person’s systolic blood pressure reading changed by an average of 12 mmHg (the unit of measurement for blood pressure) in either direction.

That’s not just a small rounding error. When you first start to take a new blood pressure medication, doctors generally expect it to lower your blood pressure by less than 12 mmHg, says one of the study’s authors, Harlan Krumholz, a cardiologist and professor of medicine at the Yale School of Medicine. That means if your doctor relies only on in-office measurements, they can’t be sure that a drop in your blood pressure is due to the medication working or to something else entirely.

Krumholz says the only way to overcome this is to collect a lot of measurements — 20 or so — and average them. Fortunately, experts say, there’s a simple way to help mitigate all of these problems: home blood pressure monitoring.

Why home blood pressure monitoring works so well

When you measure at home, you can buy a high-quality monitor with a cuff that fits your arm. You can also be sure to prepare properly and use the correct procedures when you are sitting. And you can take multiple measurements on different days — and provide that data to your doctor.

Monitoring blood pressure at home is especially valuable for anyone whose in-office readings indicate high blood pressure and for those at an elevated risk for heart disease because of preexisting health conditions like diabetes, Padwal says. It can also be useful for tracking the effect of a new medication or an adjusted dosage, or for people who are pregnant or postpartum and should be on the lookout for a severe form of high blood pressure called preeclampsia.

And not only can home monitoring be more accurate than in-office checks, but some studies have found that it can actually help you control your blood pressure, particularly in the first few months of using a monitor.

Choosing a blood pressure monitor

Buying an accurate home blood pressure monitor is key. While most manufacturers haven’t published the results from any accuracy testing, some medical groups have compiled lists of devices that have been validated by independent experts. All of the experts we talked with recommended the American Medical Association’s US Blood Pressure Validated Device Listing as a good starting point when shopping for a home monitor. Consumer Reports also rates BP monitors (though the ratings are behind a paywall).

Home blood pressure monitors come in two main varieties: those that are placed on your upper arm and those that go on your wrist. In general, experts (and CR) recommend arm monitors, which tend to be more accurate because there’s less room for error in how they’re positioned.

But using the correct arm cuff size is crucial in getting accurate readings, and some people with larger arm circumferences may not be able to find an arm monitor with an appropriate cuff size. In those cases, wrist monitors can be a good alternative. You’ll just need to take extra care to position them correctly. None of the wrist monitors in CR’s tests scored high enough to earn our recommendation, but several still earned very good accuracy scores.

You may wonder if an alternative to buying your own blood pressure monitor is to use a blood pressure kiosk in your pharmacy. But Padwal says very few public blood pressure kiosks have been validated by independent experts. Plus, it might be challenging to follow guidelines for taking blood pressure correctly when you’re in the middle of a busy pharmacy.

Copyright 2024, Consumer Reports Inc.

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