Good Medicine: How to Get Accurate Blood Pressure Readings at Home

Nearly half of American adults — 120 million people — have high blood pressure (hypertension), putting them at significant risk for stroke and heart disease. Known as the “silent killer”, hypertension contributes to more than 685,000 deaths annually in the U.S., and one in three people with the condition are unaware they have it.

Studies have shown that blood pressure readings taken in a medical office can vary widely, and may not reflect a patient’s true levels. Factors such as anxiety — often called “white coat syndrome” —  fasting before blood work, and even the time of day can markedly affect blood pressure, complicating diagnosis and treatment.

In contrast, experts have found that patients who regularly check their blood pressure at home tend to have more accurate readings. Those who discuss the results with their medical provider, either in person or via telehealth, are more successful at achieving long-term blood pressure control.

This prompted the American Heart Association (AHA), along with a dozen medical organizations, to publish medical guidelines recommending home blood pressure monitoring — not just for patients with hypertension, but for anyone with risk factors such as family history, obesity or being 65 or older.

Currently, about half of hypertensive patients monitor their blood pressure at home. In 2023, Americans spent over $430 million on home monitors.

However, home blood pressure monitoring devices can also be inaccurate. Recent research revealed that 18 million American adults are using the wrong-sized blood pressure cuff.

Blood pressure measures how forcefully blood flows through the body’s arteries. The top number, systolic pressure, is recorded as the heart beats; the bottom number, diastolic pressure, measures the pressure when the heart is resting between beats. Normal blood pressure is below 120/80 millimeters of mercury (mm Hg); hypertension is diagnosed with readings greater than 130/80 mm Hg.

Easy-to-use digital monitors typically come with an upper arm cuff that self-inflates, displaying the result on a small screen. A poorly-fitting blood pressure cuff can skew the reading by as much as 10 mm Hg: if the cuff is too small,  the readings may be falsely high, suggesting a need for medication or dosage increases. Conversely, a cuff that’s too large can result in artificially low readings, giving the erroneous impression of normal blood pressure. Those on medication might be tempted to stop treatment, which is dangerous and can lead to serious cardiac arrhythmias and rebound hypertension.

If your medical provider asks you to check home blood pressures — no prescription is needed — shop carefully. Try on the cuff and make sure it is big enough to comfortably cover about 80% of your upper arm.. Wrist and finger devices can be inaccurate and should be avoided.

Only purchase a monitor that has been FDA-approved. Among the top 100 best-selling devices, nearly 80% of upper-arm machines were not validated by the FDA. You can find a current list of authorized devices here. 

Shop wisely: You don’t have to spend a lot of money. Monitors range from $30 for a basic iHealth Track to $160 for a wireless, rechargeable phone-compatible monitor by CheckMe. Medicare and private insurance typically do not cover blood pressure monitors, though N.Y. Medicaid does as of July, 2024. 

Even a properly fitting cuff can give inaccurate readings if used incorrectly. Take your pressure in the morning before drinking caffeinated beverages, and make sure you’ve used the bathroom. Wear a short-sleeved or sleeveless shirt, and wrap the cuff around your bare arm —  rolling up long sleeves can cause artificially high readings. Sit in a straight-backed chair at a table, feet flat on the floor, and wait quietly for a minute or two before beginning. 

Take three readings, one minute apart, and write them down if your device doesn’t record them automatically. Follow up with your provider — bring your readings and your blood pressure monitor to confirm proper fit and the accuracy of your measurements.

Call your clinician urgently if your blood pressure is 180/120 or higher; call 911 if you have accompanying symptoms such as chest pain, shortness of breath, or confusion. 

Dr. Mary Jenkins, a contributor to the Herald and member of its board of directors, retired after nearly 40 years as a family practice physician in New York state.