Lower Blood Pressure Isn't Always Good

By Jane Farrell

You’ve probably heard of “white-coat hypertension,” the phenomenon of having a higher blood pressure reading in the doctor’s office when compared to the same patient’s reading outside the clinic. Now there’s another type of distorted reading that’s exactly the opposite.

Investigators say that approximately 20 to 30 percent of adults in the United States may have what’s known as “masked hypertension.” With masked hypertension, patients have lower blood pressure readings in the doctor’s office than they do outside it.

Statistics on this phenomenon have been published only over the past 15 to 20 years, according to Paul Muntner, Ph.D., lead author of the latest scientific statement on blood pressure measurement from the American Heart Association.

The statement was published in Hypertension, a journal of the American Heart Association.

“A key message from the new scientific statement is the importance of measuring blood pressure outside of the doctor’s office,” said Muntner, an epidemiologist at the University of Alabama at Birmingham School of Public Health. “Masked hypertension is associated with a high risk for heart disease and stroke. Therefore, it is important that people get their blood pressure measured correctly so they can have hypertension diagnosed and they can get started on blood pressure lowering medications.”

The statement outlines ways to accurately measure blood pressure outside of the doctor’s office in order to help the physician diagnose hypertension.

“Masked hypertension may be diagnosed through ambulatory blood pressure monitoring, which is when the patient wears a blood pressure cuff for 24 hours and has their blood pressure measured throughout the day and while they are asleep,” Muntner said. “In addition to getting a lot of measurements, this approach allows one’s blood pressure to be measured in their natural environments.”

The 2017 American College of Cardiology/American Heart Association Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure lowered the blood pressure levels used to define hypertension from 140/90 mm Hg to 130/80 Hg. It also included recommendations on how to properly take blood pressure measurements, both in and out of the doctor’s office.

Home blood pressure monitoring is recommended for people on anti-hypertensive medication.

The scientific statement from Muntner and his colleagues supports recommendations from the guideline, including using electronic devices, known as oscillometric devices, in clinical settings.

“It is now recognized that these devices are accurate and reduce the risk of human error,” Muntner said. “These are new devices that are automated and measure blood pressure multiple times in a row with a single push of a button. The AHA guideline recommends that blood pressure be taken two or more times at the doctor’s visit, but we know that is rarely done. The automated devices make it easier to do that.”

The scientific statement supports the recommendations on the best way to take your blood pressure, both at the doctor’s office and at home.

For accurate blood pressure readings, you should sit up straight in a chair with a supported back, feet flat on the floor, rest your arm on a solid surface, and not talk to anyone or look at your phone for three to five minutes before the reading is taken. You should also not smoke, drink caffeine or exercise at least 30 minutes before your blood pressure is taken.

People who measure their blood pressure at home should follow the same recommendations.

“Home blood pressure monitoring is very important and is widely recommended for people with hypertension, especially for people who are on anti-hypertensive medication,” Muntner said. “The scientific statement suggests people with hypertension measure their blood pressure two times in the morning and two times in the evening for seven days before each doctor’s visit.”

The American Heart Association continues to recommend that patients measure their blood pressure at home using a blood pressure device with an upper arm cuff that has been checked for accuracy by a health care provider.v