Blood pressure (BP) is one of the first things recorded at a doctor visit, along with your height and weight. How your blood pressure is taken can make a big difference in the accuracy of the reading. If the cuff is inflated with your arm hanging at your side or held in your lap, your blood pressure is likely to register several points higher than it really is, a recent study by researchers at The Johns Hopkins Bloomberg School of Public Health found.
Without the proper arm position and support during BP measurement, the results can overestimate BP by 4 to 10 mm Hg, and patients can end up misdiagnosed with high blood pressure.
Over 130 people in the study were randomly assigned to sets of triplicate BP measurements with the arm positioned in three ways:The higher BP readings are likely the result of the arm being below the heart, requiring the heart to pump harder.
2. With their hand supported on their lap
3. With their arm hanging unsupported at their side
The order of the three arm positions used for sets of triplicate measurements was different for each group. The number of participants in each group ranged from 12 to 31 and their mean age was 57. Just over half of the participants were female.
The study was designed to obtain multiple readings to ensure accuracy. First, participants sat seated for a 5-minute rest period with their back and feet supported. Then one set of three BP readings was taken, with measurements spaced 30 seconds apart, using an upper-arm cuff chosen based on the participant's mid-upper arm circumference.
Blood pressure was taken three times for each arm position. After the initial set of triplicate BP measurements was taken and the cuff removed, the participant walked for 2 minutes and then rested again for 5 minutes. Then another set of 3 BP readings was obtained in the same manner.
To account for the usual variability in blood pressure all participants underwent a fourth set of BP measurements with the arm supported on a desk again.
BP measurements were significantly higher when a person's arm was not optimally positioned or supported — either in their lap or hanging at their side, as often occurs when blood pressure is taken while a patient is sitting on the exam table in a doctor's office.
Readings taken while the arm was unsupported and hanging at the side overestimated systolic blood pressure (SBP) by 6.5 mm Hg and diastolic BP by 4.4 mm Hg. Supporting the arm on the lap overestimated SBP by 3.9 mm Hg and diastolic BP by 4.0 mm Hg. The results were sufficiently high to raise concerns about over-diagnosis and over-treatment.
These findings were consistent, and also more extreme, among higher-risk groups: SBP was overestimated by approximately 9 mm Hg among individuals with hypertensive BP when their arm was positioned at the side.If the office does not use the proper arm position and support during BP measurement, it can result in an overestimation of BP by 4 to 10 mm Hg, and patients can end up misdiagnosed with high blood pressure.
They also anticipate, based on calculations using data from the National Health and Nutrition Examination Survey, that improper arm position would result in 16 percent or 40 million individuals in the U.S. being misclassified as hypertensive (using a SBP cutoff of 140 mm Hg and higher). If the more current cutoff of 130 mm Hg and higher were used, it is projected that 22 percent or 54 million adults would be misclassified.
To get accurate blood pressure readings, medical offices need to make sure they are positioning patients' arms properly — on a table and level with their hearts. Out-of-office BP measurement, often conducted in the home, is important in the diagnosis and management of hypertension, so patients, too, need to make sure they are using the proper positioning for accurate BP measurements.
The study is published in JAMA Internal Medicine.
