Incorrect Arm Positions Overestimate Blood Pressure Measurements

Commonly used arm positions, such as hanging unsupported at the side or with the hand placed in the lap, for blood pressure testing can significantly overestimate levels, according to results from a new study. When compared with the guideline-recommended method for measuring blood pressure, which includes supporting the arm with a desk or table and aligning the middle of the cuff to heart level, these nonstandard arm positions overestimated systolic and diastolic blood pressure by as much as 6.5 mm Hg and 4.4 mm Hg, respectively.  

“There’s so much that depends on accurate blood pressure measurement,” senior investigator Tammy Brady, MD, PhD (Johns Hopkins University School of Medicine, Baltimore, MD), told TCTMD. “I think many of us take for granted that there's more to it than just putting on a cuff and pushing a button, but if you don't do these steps properly, you will end up with an inaccurate measurement, which has downstream consequences.”

Paul K. Whelton, MD (Tulane University School of Public Health and Tropical Medicine, New Orleans, LA), who headed up the 2017 American College of Cardiology/American Heart Association hypertension guidelines, called it an “elegantly performed study,” praising the researchers for the simple and easy-to-understand design, as well as high-quality analysis.

The new data, he told TCTMD, “underscore the findings in many other reports that following guideline recommendations for blood pressure measurement is of essential importance for the diagnosis and management of high blood pressure and hypertension.”

There are “no shortcuts” when it comes to an accurate and precise estimation of blood pressure, said Whelton. 

To obtain an accurate blood pressure reading, clinical practice guidelines state that an appropriate cuff size should be used and patients should be seated with back support, have their feet flat on the floor with legs uncrossed, and their arm appropriately placed and supported. Despite the recommendations, Brady said the correct position can be overlooked in clinical practice. Often, she said, the patient will be sitting on an examination table with the arm hanging loosely at the side or supported in their lap. Sometimes the healthcare practitioner might support the arm.

“The hypertension guidelines very clearly state that the arm needs to be supported with the cuff positioned at midheart level,” said Brady. “I think many of us know from personal experience and observation, and there have been studies to show it, that this is not routinely done.”

No Formula Able to Fix Overestimation

Published this week in JAMA Internal Medicine, the ARMS study tested the accuracy of the different ways blood pressure is routinely taken and compared results against the reference standard reflected in clinical guidelines. Designed as a crossover study, 133 participants (mean age 57 years; 53% female) had their blood pressure measured with the arm positioned in three ways: arm supported at desk (reference), hand supported in lap, and arm unsupported at side.

Study participants were randomized to one of six groups that differed in the order of the three seated arm positions. This was done to minimize any potential order effects and biases, say researchers. Blood pressure was taken with the three arm positions 30 seconds apart. After the measurements, participants had blood pressure measured again using the correct method (reference) to account for intrinsic variability in blood pressure.

Average blood pressure using the guideline-recommend method was 126/74 mm Hg, 130/78 mm Hg when the hand was placed in the lap, and 133/78 mm Hg when the arm was unsupported at the side. The lap arm position resulted in significantly higher systolic and diastolic blood pressure readings when compared with the reference standard (mean differences of 3.9 g and 4.0 mm Hg, respectively). With the arm unsupported at the side, the mean differences in systolic and diastolic blood pressure were 6.5 and 4.4 mm Hg, respectively.

These results were consistent across numerous subgroups, but systolic blood pressure was overestimated by approximately 9 mm Hg among hypertensive participants when the arm was unsupported at their side. 

Whelton noted that while systolic blood pressure was roughly 7- and 4- mm Hg higher with the two incorrect arm positions, “there was substantial variation around the average, making it impossible to use a formulaic approach in which 7 or 4 mm Hg is subtracted from systolic blood pressure readings when the patient's forearm is dangling by their side or in their lap.”  

Brady said overestimating blood pressure with these commonly used but incorrect arm positions can have a number of downstream consequences. A difference of nearly 7 mm Hg between readings could mean the difference between a borderline and a hypertensive blood pressure measurement, which would lead to another clinic visit or the use of home or ambulatory blood pressure monitoring to make the diagnosis.

“If you go the route of home blood pressure monitoring and you're not taught that you need to position your arm properly, these measurements and these errors can compound on themselves and lead to overdiagnosis,” said Brady. “There's a lot of resources being used that don't need to be used and a lot of time and money that's being expended that maybe doesn’t need to be expended.”

She said that while it might take some investment to ensure the office is configured to take blood pressure accurately, including setting up the room properly with a desk/table to support the arm, “the return on investment really has the potential to be significant.”