Blood pressure

High blood pressure (a.k.a. hypertension) is a top risk factor for some of the most common and deadly medical emergencies, including heart attacks and strokes. Consistently high pressure can damage the tissue inside your arteries, leading to plaque buildup and reducing blood flow to your heart and brain.

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.

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.

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 m ay b e too r ushed to put you i n t he r ight 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 c uff a nd p ressure g auge n eed c alibration every few months, but this rarely happens. 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 whitecoat hypertension, and about 32 percent of those with normal in-office BP readings have masked hypertension.

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. 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.

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.

— Consumer Reports Inc.