Which arm is recommended for taking blood pressure (BP) readings?

Which Arm Should Be Used for Blood Pressure Measurement?

Measure blood pressure in both arms at the first visit, then use the arm with the higher reading for all subsequent measurements. 1

Initial Visit Protocol

At the first clinical encounter, blood pressure must be measured in both arms to detect any inter-arm differences that may indicate underlying vascular pathology. 1 This bilateral measurement serves two critical purposes:

• Identifies clinically significant inter-arm differences that may suggest subclavian artery stenosis, aortic coarctation, or other arterial obstructive disease 2
• Establishes which arm provides the higher reading for consistent future monitoring 1

The right arm is traditionally preferred in children for consistency with pediatric reference tables, but this is primarily for standardization purposes rather than physiological superiority. 1

Subsequent Visit Protocol

Once bilateral measurements are obtained, always use the arm with the higher blood pressure reading for all future measurements. 1 This approach prevents underdiagnosis of hypertension and ensures accurate assessment of cardiovascular risk. 1

Key Implementation Steps:

• Document which arm has the higher reading at the initial visit 1
• Use that same arm consistently for diagnosis and treatment monitoring 1, 2
• If the difference between arms is >10 mmHg systolic, this becomes even more critical as it may indicate vascular pathology requiring further evaluation 2, 3

Clinical Significance of Inter-Arm Differences

Normal inter-arm differences are small, typically 1-3 mmHg for systolic and approximately 1 mmHg for diastolic pressure. 2 However, clinically significant differences occur more frequently than commonly recognized:

• Systolic differences >10 mmHg occur in approximately 14-20% of patients 4, 3
• Differences >20 mmHg occur in 3.5% of patients and strongly suggest vascular pathology requiring urgent evaluation 2, 3
• A 40 mmHg difference demands immediate vascular imaging to rule out subclavian stenosis, aortic dissection, or large vessel vasculitis 2

Special Circumstances

Post-Mastectomy Patients

Blood pressure can be measured in either arm after mastectomy unless lymphedema is present. 5 The mastectomy itself is not a contraindication—only active lymphedema contraindicates measurement in that limb. 5

• If lymphedema is present, use the contralateral arm 5
• If no lymphedema exists, follow the standard protocol of measuring both arms initially and using the arm with higher readings 5
• If both arms have lymphedema, consider lower extremity measurement, recognizing that leg pressures are typically 10-20 mmHg higher than brachial pressures 5, 6

Lateral Decubitus Position

When measuring blood pressure in a patient lying on their side (such as during procedures), use the non-dependent (upper) arm positioned precisely at the level of the right atrium (mid-sternum). 6 The dependent arm will produce falsely elevated readings due to hydrostatic pressure effects. 6

Critical Technical Requirements

Regardless of which arm is used, proper positioning is mandatory to avoid measurement errors:

• Support the arm at the exact level of the right atrium (mid-sternum or fourth intercostal space) 1, 6
• Never allow the arm to hang below heart level—this produces falsely high readings of approximately 2 mmHg for every inch below heart level 6, 7
• Never elevate the arm above heart level—this produces falsely low readings by the same magnitude 6, 7
• The patient must not hold their arm up—isometric muscle contraction elevates blood pressure 6, 8
• Use a cuff with a bladder that encircles at least 80% of the arm circumference 1, 6

Common Pitfalls to Avoid

• Measuring only one arm at the initial visit misses the opportunity to detect vascular disease and may lead to consistent underestimation of blood pressure if the lower-reading arm is used 1, 2
• Switching between arms for subsequent measurements introduces unnecessary variability and may mask true blood pressure changes 1
• Dismissing large inter-arm differences as normal variation without proper evaluation can miss serious vascular pathology 2
• Confusing mastectomy history with lymphedema—the surgery alone does not contraindicate blood pressure measurement 5
• Improper arm positioning (too high or too low relative to heart level) creates clinically significant errors that can lead to misdiagnosis 6, 8, 7