A recent study has uncovered that the positioning of one's arm during blood pressure monitoring, whether at home or in a medical setting, can significantly skew the results. If the arm is not aligned with the heart level and adequately supported, readings may be "markedly higher" than when the arm is correctly positioned. This could lead to a misdiagnosis of hypertension and potentially unnecessary medical interventions. The research, featured in JAMA Internal Medicine, indicates that resting the arm on the lap can cause systolic blood pressure to be overestimated by 3.9 mm Hg and diastolic by 4 mm Hg. Similarly, letting the arm hang can result in an overestimation of systolic pressure by 6.5 mm Hg and diastolic by 4.4 mm Hg.

Blood pressure is quantified in millimeters of mercury (mm Hg), with two values recorded: the systolic (the upper number) and the diastolic (the lower number). Hypertension, or high blood pressure, is diagnosed when consistent readings exceed 130/80 mm Hg.

"Medical professionals must be reminded of the necessity to adhere to proper measurement techniques," emphasized Dr. Tammy Brady, the study's senior author, who is also the vice chair for clinical research in pediatrics at Johns Hopkins University School of Medicine and medical director of the pediatric hypertension program at Johns Hopkins Children’s Center. "This study should raise awareness about the importance of correct arm positioning for accurate blood pressure readings and educate patients to advocate for accurate measurements during clinic visits," she added, noting that the findings are also relevant for home blood pressure monitoring.

The research involved 133 adults from Baltimore, Maryland, aged between 18 and 80, who had their blood pressure measured in three different arm positions: supported on a desk (the recommended position), on their lap, and hanging by their side. Each participant underwent 12 measurements for each position.

When the arm was correctly positioned on the desk, the average blood pressure reading was 126/74 mm Hg. However, when the arm was on the lap, the average reading was 130/78 mm Hg, and when hanging, it was 133/78 mm Hg. "The significant difference in readings when the arm was in the alternative positions was surprising," Dr. Brady remarked.

The study suggests that an increased vertical distance between the heart and the cuff's location can lead to higher hydrostatic pressure in the arteries due to gravity, causing an overestimation of blood pressure. Additionally, an unsupported arm may contract muscles, which can also raise blood pressure.

These findings align with prior research indicating that unsupported arm positions or positions below heart level can lead to overestimated blood pressure readings. "This study provides a more precise understanding of the impact of arm position on blood pressure readings," said Dr. Nichola Davis, vice president and chief population health officer at NYC Health and Hospitals, who was not part of the study.

For accurate measurements, the researchers highlighted several key steps in the latest clinical practice guidelines:

• Wear the correct cuff size.
• Ensure your back is supported.
• Keep your feet flat on the floor with legs uncrossed.
• Maintain the appropriate arm position—cuff at heart level with the arm supported on a desk or table.

Using the right cuff size is crucial, as an ill-fitting cuff can distort readings from automated devices. A study published in JAMA Internal Medicine last year found that standard-sized cuffs can yield "strikingly inaccurate" readings for patients who need differently sized cuffs, especially those requiring larger cuffs.

Dr. Gail Adler, a cardiovascular endocrinologist and co-specialist in the Hypertension Clinic at Brigham and Women’s Hospital, who was not involved in the new study, recommends several steps to take before a blood pressure check:

• No smoking, exercise, caffeine, alcohol, or major arguments in the 30 minutes prior.
• Sit in a chair, get in the correct position, and relax for five minutes without talking.
• Ensure your back is straight, legs uncrossed, and feet flat on the floor.
• Avoid the urge to urinate, as it can raise blood pressure.
• Do not talk during the measurement, and ensure the cuff is snug against your arm, not over clothing.

Home blood pressure measurements are often considered more reflective of a person's typical blood pressure than those taken in a clinical setting, as people tend to feel more at ease in their own homes. However, blood pressure measurements are frequently performed suboptimally in clinical practice, leading to errors that can affect medical decisions regarding blood pressure management in 20% to 45% of cases, according to the American Medical Association.

"I believe we are not aggressive enough in treating hypertension in the United States," said Dr. Dave Montgomery, a cardiologist at Piedmont Healthcare in Atlanta, who was not involved in the study. "Hypertension is a common risk factor for cardiovascular disease and is one of the easiest to treat and control. Yet, it remains a significant contributor to cardiovascular issues and mortality."

Dr. Montgomery also noted that a blood pressure reading that may be off by 4 to 5 mm Hg due to arm position is unlikely to lead to overdiagnosis or overtreatment. "If someone has normal blood pressure, a 4 mmHg difference won't change that. However, in someone with hypertension, a 5-10 point difference may indicate that we need better control," he said. "Blood pressure can fluctuate minute by minute due to physical activity and emotional states. Therefore, we should not hastily judge based on a single reading. Consistently high blood pressure should be treated aggressively to reduce the burden of heart disease."

High blood pressure increases the risk of heart disease and stroke, which are leading causes of death in the United States. Nearly half of US adults have high blood pressure, but only about one in four with high blood pressure has it under control, according to the US Centers for Disease Control and Prevention.