Many people trust blood pressure readings to show whether their heart is healthy. However, new research from Johns Hopkins Medicine has found that a very small detail during the test can change the result.
Simply placing your arm in the wrong position may make your blood pressure look higher than it really is, which could lead to an incorrect diagnosis of high blood pressure.
Blood pressure is measured with two numbers. The top number, called systolic blood pressure, shows the pressure when the heart pumps blood. The bottom number, called diastolic blood pressure, shows the pressure when the heart relaxes between beats.
Doctors use these numbers to decide whether someone has healthy blood pressure or may need treatment for hypertension.
High blood pressure often has no clear symptoms, but it greatly increases the risk of heart disease, stroke, kidney disease, and other serious health problems. Because of this, doctors rely on accurate blood pressure readings when making decisions about medicines and lifestyle changes. Even a small error can make a difference.
In the new study, researchers wanted to find out how arm position affects blood pressure readings. They compared three common positions. One group rested their arm on a desk at heart level, another rested the arm on their lap, and a third let the arm hang down without any support.
The researchers found that the correct method was to support the arm at the same height as the heart. When the arm hung down, systolic blood pressure was about 6.5 points higher and diastolic blood pressure was about 4.4 points higher than the correct reading.
Resting the arm on the lap also produced readings that were too high, with systolic pressure about 3.9 points higher and diastolic pressure about 4.0 points higher.
These differences may seem small, but they can have important consequences. For example, a person whose true systolic pressure is 123 could be measured at around 130 because of poor arm positioning. That higher reading could lead to a diagnosis of stage 1 hypertension and possibly unnecessary treatment or worry.
The study included 133 adults between 18 and 80 years old. Each participant had their blood pressure measured several times using automatic blood pressure monitors, similar to those commonly used in clinics and homes. Everyone followed the same preparation steps, including resting quietly before the test, to make sure the results were reliable.
Dr. Tammy Brady, who led the research, said that correct arm position is essential for getting an accurate blood pressure reading. Researcher Sherry Liu added that people who feel perfectly healthy could still receive an incorrect diagnosis if their arm is not supported properly during the test.
The researchers recommend always resting the arm on a table or other firm surface so that it is level with the heart during a blood pressure check. Patients can also help by asking for proper arm support during clinic visits and by following the same method when checking blood pressure at home.
Measuring blood pressure the same way each time also helps produce more reliable results because stress, caffeine, smoking, exercise, and the time of day can all affect the numbers.
The study was published in JAMA Internal Medicine. The findings show that paying attention to a simple detail can improve the accuracy of blood pressure measurements and help doctors make better decisions about a person’s health.
If you care about high blood pressure, please read studies about what to eat and to avoid for high blood pressure, and 12 foods that lower blood pressure.
For more health information, please see recent studies about the connection between potato and high blood pressure, and how to eat your way to healthy blood pressure.
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