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Arm Position and BP Readings
Quick Takes
- Proper BP measurement necessitates having the arm positioned at heart level and supported on a desk or table.
- Supporting the arm on the lap gives BP readings 3.9/4.0 mm Hg higher than with proper positioning.
- Having the arm dangle at the side gives BP readings 6.4/4.4 mm Hg higher than with proper positioning.
- Improper arm positioning during BP measurement inappropriately increases the diagnosis of hypertension and, therefore, may lead to addition of unnecessary medications.
Study Questions:
How important is proper arm position in obtaining accurate blood pressure (BP) measurements?
Methods:
A total of 133 subjects in the ARMS crossover randomized clinical trial had their BP measured in triplicate under three conditions: 1) arm supported on a desk with cuff at heart level (the proper way), 2) hand supported on lap, and 3) arm dangling on the side of the body. A fourth reading was made with proper positioning, just to account for intrinsic variability. The ARMS population included adults between 18-80 years of age without any conditions such as rashes, casts, sores, shunts, or arm circumference >55 cm. The group analyzed was 53% female, had an average age of 57 years, and 41% had a body mass index of >30 kg/m2. The primary outcomes were systolic and diastolic differences between the lap supported readings and the readings with proper technique, and the side supported readings and the readings with proper technique.
Results:
BP was, on average, 3.9/4.0 mm Hg higher when readings were taken with the hand on the lap, rather than using the proper technique of having the arm supported on a desk. Readings were 6.5/4.4 mm Hg higher when the arm was dangling at the side of the body compared to being supported on a desk. Subgroup analyses that included difference in baseline BP, age, obesity, and health care utilization yielded no differences.
Conclusions:
Measurement of BP without the arm properly supported, as described in the 2017 American College of Cardiology/American Heart Association (ACC/AHA)/multisociety guideline for management of high BP (linked here), can result in significant increases in the reported readings: 3.9/4.0 mm Hg with hand on lap and 6.5/4.4 mm Hg with arm dangling on the side. These inaccuracies in readings can result in overtreatment of BP, increased potential of side effects from BP medications because of hypotension, and under-reporting of successful achievement of system-wide BP management.
Perspective:
This study is truly of great interest to any provider who manages BP in their practice. However, it is an unfortunate reality that there would even be an interest in performing a study that, essentially, asks whether taking BP in an inappropriate way, inconsistent with published national guidelines, is okay to do. The reason, quite obviously, is that incorrect BP management is rampant in our health care system and that a huge number of medical judgments are made on data that are often obtained in a slipshod fashion for various reasons, not the least being time pressure in rooming a patient.
I have great recollections of having my BP taken over a winter jacket at a health fair, with my arm dangling in a dental chair with an unvalidated wrist device, while being weighed and having a history taken on the way to an exam room, and with cuffs of greatly inappropriate sizes. It is no wonder that the first recommendation of the 2017 ACC/AHA/multispecialty guideline for management of high BP describes, in great detail, how to take BP appropriately, as you simply cannot make good clinical judgments without good clinical data. In the same way that we would not accept blood tests done without controls or electrocardiograms done over a flannel shirt (presumably because of time pressure), we should insist that our patients have their BP measured properly. BP measurement should be considered an important medical test and performed with the same precision and seriousness as all other medical tests.
This study is very illuminating in that it shows that a seemingly small but common variance from proper BP measurement can yield inaccuracies that are truly clinically significant and at a magnitude that can potentially drive improper medical care. It is well-worth re-reading section 4.1 of the 2017 ACC/AHA BP guideline (linked here) as a refresher in proper BP measurement. Additionally, section 4.2 (home readings) may also be of interest, as there is growing interest, consistent with the recently published European Society of Cardiology guidelines, in using home readings for management in patients who are able to provide them.
Clinical Topics: Prevention, Hypertension
Keywords: Antihypertensive Agents, Blood Pressure, Hypertension
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