Blood pressure measurements are a standard part of both routine and urgent health visits—but most Americans aren't aware of what constitutes a normal or healthy blood pressure reading, new research shows.

The news comes from a study published last month in the journal Medical Decision Making, which found that, despite feeling confident in their blood pressure knowledge, the majority of Americans did not know the upper threshold for normal or healthy blood pressure readings, which is 120/80 mm Hg (millimeters of mercury).

“Blood pressure is taken at almost every doctor’s visit, but there is little rudimentary education about blood pressure in the office because visits often focus on other topics, typically whatever a patient is there for,” lead study author Wändi Bruine de Bruin, PhD, Provost Professor of Public Policy, Psychology, and Behavioral Science at University of Southern California, told Health.

More than half of U.S. adults are living with hypertension, or high blood pressure, but only about a quarter of those people have it under control. And though it’s a common conditions, it’s also deadly—high blood pressure increases the risk of both heart disease and stroke, two leading causes of death for Americans.

But because high blood pressure doesn’t typically cause symptoms (it’s often referred to as the “silent killer”) the only real way to know if you have it is through routine blood pressure measurements—and even then, personal knowledge of normal or healthy blood pressure readings can either benefit or hinder future health outcomes.

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For the new study, Bruine de Bruin and her team surveyed more than 6,500 U.S. adults, regarding their knowledge about blood pressure readings, and their confidence in that knowledge.

The sample included 1,342 adults who had hypertension without comorbidities and 795 who had hypertension with comorbidities, like heart disease, kidney disease, or diabetes; the authors adjusted for socioeconomic status, level of education, and hypertension diagnosis.

Overall, 64% of those surveyed expressed confidence in their knowledge of blood pressure readings—but only 36% correctly stated that 120/80 mm Hg was the upper limit for a healthy or normal blood pressure reading.

The discrepancies between people being confident they understood the readings and accurately identifying healthy readings were even greater in the groups who had high blood pressure. Among those who had hypertension alone, 78% were confident they understood the readings, while just 47% did. Among participants with both hypertension and comorbidities, 81% were confident they understood while just 40% were accurate. 

The researchers also found that patients who were confident they understood blood pressure readings were more likely to say they’d seek interventions for stage 2 hypertension readings, but were less likely to take the same action for stage 1 readings.

According to researchers, this overconfidence—and thus, unwillingness to act—could be negatively affecting their health outcomes.

“The most worrying finding is that most people don’t know what normal or healthy blood pressure is,” Bruine de Bruin said, “yet they are confident that they do know and that can undermine their willingness to seek care.”

Blood pressure readings include two numbers. The first, systolic blood pressure, measures the pressure in your arteries when your heart beats, pushing blood through the body. The second, diastolic blood pressure, measures the pressure in your arteries between beats. Generally, the lower the numbers, the better. 

The American Heart Association and American College of Cardiology updated the threshold for healthy blood pressure in 2017, following the SPRINT (Systolic Blood Pressure Intervention Trial) clinical trial, which found the upper threshold of healthy blood pressure to be less than 120/80 mm Hg.

(This is lower than previously thought, and it’s common for clinics to use the old threshold of 130/80 mm Hg, said Willie E. Lawrence Jr., MD, FAHA, FACC, a cardiologist and medical director of the Center for Better Health and Wellness in Benton Harbor, Michigan.)

But even healthcare professionals can—and often do—get inaccurate readings. “Most clinics do a horrible job of measuring blood pressure,” Dr. Lawrence said, noting that it’s important for patients to educate themselves about the appropriate way to measure blood pressure so they can advocate for themselves in the clinic.

To get an accurate blood pressure reading, health care providers should wait five minutes after the patient moves from the waiting room to the examination room before taking the reading, Dr. Lawrence said. Best practices also include making sure the patient’s legs are not crossed and ensuring their arm is at the same level as the device. They also shouldn’t have a full bladder, be talking or actively listening to someone talking, have an unsupported back, or be using a cuff that is too small.

“The patient needs to know what physicians should be doing, it’s their health,” Dr. Lawrence said, adding that patients should feel comfortable asking their health care provider to correct any mistakes.

If you’re using an at-home device to check your blood pressure, Dr. Lawrence said the first place to start is with a validated device.

“If you don’t start with a validated device for home measurement, you are not likely to get good blood pressure control,” he said.

The website has a list of tested and validated at-home blood pressure devices. If you do choose to monitor yourself at home, Dr. Lawrence recommends starting here, and then following the same guidance—sitting still in a quiet room, not talking, ensuring your cuff isn’t too small—to ensure an accurate reading. 

After that, understanding what the healthy thresholds for high blood pressure are will help a patient advocate for themselves if their reading is high.

“As a patient, it’s important to know what the cutoffs are so if you notice at the doctor’s office that you are above those cutoffs, you can bring it up during your visit,” Bruine de Bruin said.

As people age, their arteries and blood vessels stiffen, making high blood pressure more common, said Dr. Lawrence. This is virtually inevitable; but diet, exercise, and comorbidities, especially diabetes, all elevate a person’s risk of developing high blood pressure, and lifestyle changes are almost always part of treatment.

“The foundation for hypertension is lifestyle intervention. But for people who have had poor habits that predisposed them to hypertension, it can be hard to sustain new habits,” Dr. Lawrence said. “They aren’t going to change those numbers overnight.”

For this reason, most people who have blood pressure readings that fall into stage 1 or higher will also require medication. The general guidance is one medication, which relaxes the blood vessels, for stage 1 hypertension, and two medications—usually diuretics, beta-blockers and alpha-blockers, calcium channel blockers, or ACE inhibitors—for stage 2.

“People might think that they are a failure if they can’t make changes in blood pressure with lifestyle changes, but we need to treat high blood pressure as the chronic disease it is, meaning treat it with the medication it needs,” Dr. Lawrence said. “That’s not a failure.”

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