Arm Position Significantly Affects Accuracy of Blood Pressure Readings, Study Finds

A new clinical trial conducted by researchers at Johns Hopkins University has revealed that improper arm positioning during blood pressure measurements can lead to significantly higher readings, potentially misclassifying millions of adults as having high blood pressure. Published in JAMA Internal Medicine on October 7, the study emphasizes the importance of proper arm placement to ensure accurate readings.

Blood pressure, measured in millimeters of mercury (mm Hg), consists of two readings: systolic (the pressure exerted when the heart beats) and diastolic (the pressure when the heart rests between beats). The trial found that participants with their arm resting on their lap or hanging by their side experienced skewed readings. When the arm was positioned on the lap, systolic and diastolic readings were, on average, 4 mm Hg higher than when the arm was supported at heart level, which is the recommended position. For participants with their arm hanging by their side, the systolic readings increased by an average of 7 mm Hg, and diastolic by 4 mm Hg.

Given that an estimated 120 million adults in the United States have high blood pressure—defined as readings equal to or above 130/80 mm Hg—accurate readings are crucial. High blood pressure increases the risk of cardiovascular diseases and stroke, and the study highlights that improper arm positioning could lead to inflated numbers and potentially unwarranted diagnoses. In fact, based on national survey data, the researchers estimate that 54 million adults might be misclassified if their arm is not positioned correctly.

Current medical guidelines for accurate blood pressure readings recommend keeping the arm supported at heart height, using a properly fitting blood pressure cuff, and ensuring legs are uncrossed, feet flat, and back supported. However, the study notes that adherence to these guidelines in clinical settings may vary, underscoring the need for standardized practices to avoid inaccurate readings.