• In a new study, researchers say different arm positions can produce different blood pressure readings.
• They report that blood pressure readings taken when the arm is resting on a hard surface such as a desk are slightly lower than when the arm is resting in a person’s lap or hanging by their side.
• Experts say inaccurate higher readings could lead to a hypertension misdiagnosis and unnecessary interventions like medication.

Does it really matter whether your arm is resting on your lap or hanging by your side when you have your blood pressure taken? Experts say it just might.

In a new study published in JAMA Internal Medicine, researchers say three different arm positions produced three different blood pressure readings with a difference of 4 to 7 points on the top and bottom numbers.

The researchers found that blood pressure taken while a person’s arm is resting on a hard surface such as a desk or arm chair produced the most accurate readings.

If a person’s actual top number on a blood pressure reading is 115, an incorrect arm position could increase that mark to more than 120, pushing them into the category of elevated blood pressure. If someone’s actual measurement is 126, a misreading could bump that number above 130 and into the category of stage 1 hypertension.

Experts say not only would a person be misdiagnosed with high blood pressure, they could also be prescribed unnecessary medication.

“This is a very practically useful study that reiterates the importance of proper blood pressure measurement technique in order to obtain the most accurate blood pressure readings,” said Cheng-Han Chen, MD, an interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in California.

“This study shows that seemingly small differences in blood pressure measurement technique can affect blood pressure readings. While a 4-to-7 point difference in a blood pressure reading may not seem like a lot, it is enough to push someone’s blood pressure into a higher category, such that they may end up being started on a blood pressure medication that they might not need,” Chen, who wasn’t involved in the study, told Healthline.

Different arm positions change blood pressure readings

For their study, researchers looked at 133 adults between the ages of 18 and 80. The average age was 57.

About 53% of the participants were female, 77% were Black, and 41% had a body mass index (BMI) of 30 or higher, which classifies them as having obesity.

In addition, 36% of participants had a top blood pressure number of 130mm HG or higher at the start of the study.

The researchers measured the participants’ blood pressure while people held their arms in three different positions:

• resting on their lap
• laying on a hard surface
• hanging along the side of their body

All the participants had their blood pressure taken with all three arm positions, but they were randomly assigned to one of six groups that differed in what order the measurements were taken.

By the study’s end, researchers concluded that blood pressure readings taken while the arm was supported on a surface such as a desk or chair arm were lower than the measurements taken when the arm was in a lap or hanging by the side.

“This research highlights the importance of utilizing correct technique and arm positioning in order to obtain accurate blood pressure measurements in a real-world clinical setting,” said Megan Kamath, MD, a cardiologist at UCLA Health in California who was not involved in the study.

“In the 2017 U.S. hypertension guidelines, categorization for stages of hypertension vary by increments of 10 mmHg, so one can imagine that a difference of 4 to 7 mmHg can make a significant difference in moving someone to a different level of categorization, which has implications for both treatment of hypertension and lifetime cardiovascular risk,” Kamath told Healthline.

Small changes in blood pressure numbers matter

A blood pressure reading measures the total amount of force your blood pushes across the walls of your arteries.

The top, or systolic, number indicates the pressure on the artery walls as your heart beats. The bottom, or diastolic, number determines the pressure when your heart rests between beats.

When taking blood pressure measurements, the American Heart Association (AHA) recommends:

• avoiding caffeine, smoking, and exercise for 30 minutes beforehand
• positioning a blood pressure cuff on the upper arm at mid-heart level
• placing feet flat on the floor with the back supported

In their study, researchers found that systolic pressure was 6.5 points higher when participants had their arms dangling by their side compared to when their arms rested on a desk. The diastolic number was 4.4 points higher with the arm hanging by the side.

When participants’ arms were on their laps, the systolic reading was 3.9 points higher than in the supported position. The diastolic pressure was 4 points higher.

“Incorrect positioning can result in up to 7 mm Hg error in the measurement,” said Eugene Yang, MD, a professor of cardiology and medicine at the University of Washington School of Medicine and member of the American Heart Association’s HTN and KCVD Hypertension Science Committee. Yang wasn’t involved in the study.

“This can have significant consequences when making decisions about whether someone needs to be treated for hypertension,” he told Healthline. “Furthermore, when this error is compounded by other mistakes, such as not waiting 5 minutes before taking a measurement or making sure your feet are flat on the ground, the impact on the readings could be even more substantial,” Yang continued.

Kamath stressed the importance of obtaining accurate blood pressure readings.

“This research highlights the importance of taking quality measurements to ensure that our patients are treated appropriately based on these findings,” she said.

“Hypertension is a significant risk factor in cardiovascular disease and has significant implications for both prevention and treatment of disease across the lifespan so it is crucial for healthcare professionals to recognize potential inconsistencies and address them.”

Accurate blood pressure readings at home are equally important. “Patients taking their blood pressure at home using a home cuff should remember to always take it with the arm in a supported position,” Chen said.

Kamath noted the research also provides important information for patients. “This study should encourage patients to be advocates in their own healthcare,” she said. “Patients should feel empowered to ask for a repeat blood pressure measurement if the measurement being obtained is significantly different than previously obtained.”

Yang agreed. “The techniques of blood pressure measurement in the office also apply to patients at home,” he said.

“Mistakes made at home will also translate to incorrect readings that possibly lead to overtreatment of blood pressure based on these measurements. Clinicians have a responsibility to educate their patients on how to measure their blood pressures correctly at home,” Yang noted.

What to know about high blood pressure

Nearly half of adults in the United States have high blood pressure, according to the Centers for Disease Control and Prevention (CDC).

A higher percentage of males have high blood pressure compared to females.

High blood pressure is also more common in non-Hispanic Black adults than in non-Hispanic white adults, non-Hispanic Asian adults, and Hispanic adults.

High blood pressure, also known as hypertension, puts a person at a higher risk of heart disease and stroke. The CDC estimates that in 2022 high blood pressure was a primary or contributing cause of 685,875 deaths in the United States.

High blood pressure doesn’t always cause symptoms. Sometimes symptoms don’t appear until someone has had hypertension for years. When they do manifest, symptoms may include:

• skin flushing
• red spots in front of the eyes
• dizziness

There are ways to lower your risk of high blood pressure. The CDC lists these strategies:

• eat a healthy diet with plenty of fruits and vegetables
• maintain a healthy weight
• stay physically active (aim for a minimum of 2.5 hours of moderate-intensity exercise per week)
• don’t smoke
• limit your alcohol intake
• get adequate sleep

“People looking to avoid developing high blood pressure should eat a healthy balanced diet low in sodium, engage in regular physical activity, get an adequate amount of quality sleep, maintain a healthy weight, avoid alcohol and tobacco, and reduce their stress levels,” Chen recommended.

Takeaway

Researchers report that arm position can make a difference during blood pressure readings.

They found slightly lower blood pressure numbers when a person’s arm is laying on a hard surface such as a desk compared to the arm resting in a person’s lap or dangling by their side.

Experts say this variation in numbers could be the difference between someone being diagnosed with high blood pressure and prescribed unnecessary medication.