An improper arm position can distort blood pressure readings.

Blood pressure readings must be administered while supporting a patient’s arm at around heart level, according to Tunvarat Pruksachat/Moment RF/Getty Images (https://bit.ly/1zO4QRq)
Think back to when you last had your blood pressure taken: how were you sitting, where exactly was the cuff, and what activity were your arms engaged in? Most of us take blood pressure readings so routinely, we barely give much thought about any potential missteps that may cause inaccurate readings – however even minor discrepancies could give an inaccurate reading due to several reasons, from incorrect cuff sizes, crossed legs on an exam table to simply stress of being at clinic (known as white coat hypertension) which could raise or lower results dramatically.
Now add another common gaffe: holding your arm improperly. Researchers from Johns Hopkins University recently conducted an experiment which demonstrated how simply deviating from guidelines regarding arm position can result in an inaccurate estimate of blood pressure for any given patient. Dr. Tammy Brady of Johns Hopkins University School of Medicine and senior author of this research study published Monday by JAMA Internal Medicine was among those concerned that false readings might even cause misdiagnosis of hypertension and decisions to start medication treatment for it. People often take blood pressure screening for granted,” notes Brady, but decisions often hinge on its results. For the trial, over 130 adults underwent three distinct blood pressure measurements using automated devices – all three scenarios measured their BP simultaneously. The first participant complied with all guidelines: They supported their arm on a desk with its cuff placed approximately at “mid-heart level” on their arm. Brady observed two deviations from protocol during these measurements: arms either resting on patient laps or hanging at their side produced large overestimates of blood pressure readings.
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An arm resting on their lap could inadvertently raise both of the top and bottom numbers — known as systolic and diastolic pressure respectively — by about 4 millimeters of mercury (mmHg), the unit of measurement for blood pressure. When arms were rested at their sides, this phenomenon became even more obvious, increasing systolic blood pressure by 6.5mmHg while simultaneously decreasing bottom blood pressure by 4.4 mmHg. Although it might not seem significant at first, it should concern anyone that data used to assess risk for cardiovascular disease could become inaccurate due to such an avoidable error. An individual whose systolic blood pressure falls into the elevated range between 120-129 may inadvertently enter into hypertensive territory by placing their arm incorrectly; such misclassification begins at 130mmHg. “This is very basic but hopefully reminds everyone how critical blood pressure readings can be,” states Brady’s team, having conducted numerous studies into inaccurate readings that lead to misdiagnosis or incorrect prescribing of medication for someone who doesn’t actually need it at all. Guidelines for accurately measuring blood pressure outlines several steps designed to provide the most precise reading: It should be quiet; five minutes must pass between taking measurements and entering the bathroom beforehand, keeping both feet on the ground with their back supported; amongst others. “Even though we know exactly what to do, making these strategies come together has proven challenging,” according to Dr. Stephen Juraschek of Beth Israel Deaconess Medical Center in Boston and director of their Hypertension Center. Of course, some details might get neglected during a hectic daily rush to see patients; research also shows new physicians aren’t getting proper training either. A major barrier lies within exam rooms themselves which don’t make taking blood pressure easy (even Brady herself needs to rearrange furniture before seeing patients!).
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Juraschek believes this latest research clearly establishes arm position as “essential.” A dangling arm usually isn’t isolated – errors tend to compound and compound themselves into inaccuracy over time, such as seeing people reduce 20mmHg net reduction; that can have significant impacts on therapy decisions as he notes “I think when all these features combine, the impact can really become felt by patients”.