A recent study has confirmed that having the arm in the wrong position during blood pressure checks may lead to readings markedly higher than when it is in the recommended position: appropriately supported on a table with the middle of the cuff positioned at heart level.
Otherwise, said the researchers, there might be misdiagnosis of high blood pressure, possibly leading to unnecessary treatment.
The study, published in JAMA Internal Medicine, found that having the arm resting in the lap during a check can lead to an overestimated systolic BO measurement by 3.9mm Hg and overestimated diastolic reading by 4mm Hg. And having the arm hanging down can lead to an overestimated systolic reading by 6.5mm Hg and overestimated diastolic reading by 4.4mm Hg.
“Healthcare providers need to be reminded about the importance of taking the time to do these steps properly,” said the study’s senior author Dr Tammy Brady, who serves as vice-chair for clinical research in the department of paediatrics at the Johns Hopkins University School of Medicine and medical director of the paediatric hypertension programme at Johns Hopkins Children’s Centre.
CNN reports that for the study, the Johns Hopkins researchers recruited 133 adults between August 2022 and June 2023, who were randomly assigned to have their BP measured while their arms were positioned in three different ways: supported on a desk, as is the recommended standard practice; supported on their lap; or hanging by their side, unsupported.
Each participant underwent a total of 12 BP measurements with their arms in each position.
When their arms were supported on a desk as recommended by the standard clinical guidelines, the average BP reading was 126/74, the researchers found.
But when their arms were resting in their laps during their readings, the average reading was 130/78, and when their arms were hanging by their sides, the average was 133/78.
“I did not expect there to be that much of a difference,” Brady said. “We were surprised by how much of a difference there was.”
The researchers wrote that there are several physiological reasons why readings could be erroneously higher when the arm is not adequately positioned or supported. A greater vertical distance between the heart and where the cuff is placed can increase hydrostatic pressure in the arteries, or the pressure of the blood against the wall, due to gravity’s pull, leading to an overestimation of blood pressure.
And an unsupported arm can lead to the muscle contracting, which may cause an increase in blood pressure.
The latest findings are consistent with previous research that has shown unsupported arm positions or the arm being positioned below heart level can overestimate a reading.
“We know that arm position affects the blood pressure reading, but what this study does is give a more precise measure of just how much this has an impact,” said Dr Nichola Davis, vice president and chief population health officer at NYC Health and Hospitals, who was not involved in the study.
“This is seen in participants with all levels of blood pressure, but more pronounced in those with elevated blood pressure.”
The researchers wrote wearing the appropriate cuff size is key because an improperly sized blood pressure cuff can distort blood pressure readings taken by automated BP devices.
A study published last year in JAMA Internal Medicine found that using standard, regular-sized cuffs resulted in “strikingly inaccurate” readings if a patient required differently sized ones, particularly for those needing larger ones.
It’s estimated that nearly half of all adults in the United States have high blood pressure, but only about one in four with high blood pressure has their BP under control, according to the US Centres for Disease Control and Prevention (CDC).
“I don’t think that we are aggressive enough with the treatment of hypertension in America,” said Dr Dave Montgomery, a cardiologist at Piedmont Healthcare in Atlanta, who was not involved in the new study.
Regarding the study, however, he added that he doesn’t see a blood pressure reading that may be off by 4 to 5 mm Hg – due to arm position – leading to overdiagnosis or overtreatment, in the form of a new prescription or dose modification.
“If someone has normal blood pressure, 4 mmHg won’t change that. But in someone with a diagnosis of hypertension, 5-10 points may signal that we don’t quite have the control we seek.”
He added that blood pressure can change minute by minute, due to physical factors and someone’s psycho-emotional states.
“This means that in general, we shouldn’t make hasty judgments about one blood pressure reading. But consistently high blood pressure should be treated aggressively,” he said. “This is how we lower the burden of heart disease.”
Study details
Arm Position and Blood Pressure Readings: The ARMS Crossover Randomised Clinical Trial
Hairong Liu, Di Zhao, Ahmed Sabit, et al.
Published in JAMA Internal Medicine on 7 October 2024
Abstract
Importance
Guidelines for blood pressure (BP) measurement recommend arm support on a desk with the midcuff positioned at heart level. Still, nonstandard positions are used in clinical practice (eg, with arm resting on the lap or unsupported on the side).
Objective
To determine the effect of different arm positions on BP readings.
Design, Setting, and Participants
This crossover randomised clinical trial recruited adults between the ages of 18 and 80 years in Baltimore, Maryland, from August 9, 2022, to June 1, 2023.
Intervention
Participants were randomly assigned to sets of triplicate BP measurements with the arm positioned in 3 ways: (1) supported on a desk (desk 1; reference), (2) hand supported on lap (lap), and (3) arm unsupported at the side (side). To account for intrinsic BP variability, all participants underwent a fourth set of BP measurements with the arm supported on a desk (desk 2).
Main Outcomes and Measures
The primary outcomes were the difference in differences in mean systolic BP (SBP) and diastolic BP (DBP) between the reference BP (desk 1) and the 2 arm support positions (lap and side): (lap or side − desk 1) − (desk 2 − desk 1). Results were also stratified by hypertensive status, age, obesity status, and access to health care within the past year.
Results
The trial enrolled 133 participants (mean [SD] age, 57 [17] years; 70 [53%] female); 48 participants (36%) had SBP of 130 mm Hg or higher, and 55 participants (41%) had a body mass index (calculated as weight in kilograms divided by height in meters squared) of 30 or higher. Lap and side positions resulted in statistically significant higher BP readings than desk positions, with the difference in differences as follows: lap, SBP Δ 3.9 (95% CI, 2.5-5.2) mm Hg and DBP Δ 4.0 (95% CI, 3.1-5.0) mm Hg; and side, SBP Δ 6.5 (95% CI, 5.1-7.9) mm Hg and DBP Δ 4.4 (95% CI, 3.4-5.4) mm Hg. The patterns were generally consistent across subgroups.
Conclusion and Relevance
This crossover randomised clinical trial showed that commonly used arm positions (lap or side) resulted in substantial overestimation of BP readings and may lead to misdiagnosis and overestimation of hypertension.
JAMA Network article – Effects of Cuff Size on the Accuracy of Blood Pressure Readings (Open access)
See more from MedicalBrief archives:
Kids’ blood pressure measures ‘substantially different’ between arms
Checking BP in doctor’s rooms not always ideal
Blood pressure: standing readings outperform seated
Inter-arm difference in BP robustly linked to greater early death risk