Many people trust blood pressure readings as an important sign of their health.
Doctors use these numbers to decide whether a person may have high blood pressure, also called hypertension, which is one of the leading causes of heart disease and stroke around the world.
However, a new study from Johns Hopkins Medicine shows that a very small detail during the test could greatly change the result. Something as simple as where a person rests their arm may cause blood pressure readings to appear much higher than they really are.
The discovery is important because millions of people have their blood pressure checked every day in clinics, pharmacies, and at home.
If the reading is too high because of poor arm positioning, some people could be wrongly told they have high blood pressure. This could lead to stress, extra medical tests, or even medicine they may not actually need.
Blood pressure readings contain two numbers. The first number is called systolic blood pressure. It measures the pressure inside the arteries when the heart pumps blood through the body. The second number is called diastolic blood pressure, which measures the pressure when the heart rests between beats.
Doctors generally consider a systolic blood pressure reading of 130 or higher to be high. A person with readings at this level may be diagnosed with stage 1 hypertension, a condition linked to a greater risk of heart attacks, strokes, kidney disease, and other serious health problems.
In the new study, researchers wanted to find out how arm position changes blood pressure readings. They tested three common arm positions during blood pressure checks.
In the first position, the arm was properly supported on a desk or table at heart level. In the second position, the arm rested on the person’s lap. In the third position, the arm was left hanging down by the side without any support.
The researchers discovered that unsupported arm positions caused blood pressure readings to rise higher than they should. The largest difference happened when the arm was hanging freely by the side.
In this position, systolic blood pressure readings increased by an average of 6.5 points, while diastolic pressure increased by 4.4 points compared with the correct arm position.
Even resting the arm on the lap created inaccurate readings. Compared with the correct supported position, systolic pressure was about 3.9 points higher and diastolic pressure was about 4 points higher.
These differences may sound small, but they can have a major effect on medical decisions.
For example, a person whose real systolic blood pressure is around 123 could mistakenly receive a reading close to 130 if their arm is not properly supported. That difference could change the diagnosis from normal blood pressure to hypertension.
The researchers explained that blood pressure should always be measured with the arm supported at heart level. Usually, this means placing the arm on a desk, table, or armrest while sitting comfortably and quietly.
However, this simple rule is often ignored in busy clinics and medical offices. Many people use automatic blood pressure machines where they sit alone without guidance. In some cases, there may not even be a table nearby to support the arm correctly.
Dr. Tammy Brady, who led the study, said that arm position is a major factor in getting accurate blood pressure readings. Another researcher, Sherry Liu, explained that people who feel perfectly healthy and have no symptoms might still receive a false diagnosis simply because their arm was placed incorrectly during the test.
The study included 133 adults between 18 and 80 years old. To make the results fair and reliable, all participants followed the same preparation steps before testing.
For example, they rested quietly and used the bathroom before their blood pressure was measured. Each participant had their blood pressure checked several times in different arm positions, similar to how blood pressure is measured during a regular doctor visit.
The researchers mainly studied automatic blood pressure machines, which are now commonly used both in clinics and in homes.
Although the findings may not apply exactly the same way to manual blood pressure checks using a stethoscope, the researchers still recommend following the correct arm position no matter which method is used.
Blood pressure is naturally affected by many everyday factors. Stress, nervousness, exercise, smoking, caffeine, pain, and even the time of day can change the numbers. This is why doctors recommend measuring blood pressure in a calm and consistent way each time.
The researchers hope the study will encourage both healthcare workers and patients to pay more attention to proper testing methods.
Dr. Brady said patients should feel comfortable asking for a table or another surface to support their arm during the test. People checking their blood pressure at home should also make sure their arm is supported and level with their heart.
The study is a reminder that small details in healthcare can sometimes make a very big difference. A simple change in arm position may help avoid wrong diagnoses and ensure that patients receive the most accurate information about their heart health.
Accurate blood pressure readings can help doctors and patients make better decisions and avoid unnecessary worry or treatment.
If you care about high blood pressure, please read studies that early time-restricted eating could help improve blood pressure, and natural coconut sugar could help reduce blood pressure and artery stiffness.
For more information about blood pressure, please see recent studies about How to eat your way to healthy blood pressure and results showing that Modified traditional Chinese cuisine can lower blood pressure.
The study was published in the journal JAMA Internal Medicine.
Copyright © 2026 Knowridge Science Report. All rights reserved.
