Which arm is best for checking blood pressure?

Which Arm to Use for Blood Pressure Measurement

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

Initial Visit Protocol

At the first clinical encounter, bilateral arm blood pressure measurement is mandatory to detect inter-arm differences that may indicate underlying vascular pathology such as subclavian artery stenosis, aortic coarctation, or other arterial obstructive disease. 1 The American Heart Association explicitly recommends this approach to prevent underdiagnosis of hypertension and ensure accurate cardiovascular risk assessment. 1

What Constitutes a Significant Difference

• Normal inter-arm differences are minimal: typically 1-3 mmHg for systolic and approximately 1 mmHg for diastolic pressure 1, 2
• Clinically significant threshold: A systolic difference ≥10 mmHg warrants using the higher-reading arm for all future measurements 2
• Urgent evaluation threshold: A difference ≥20 mmHg strongly suggests vascular pathology requiring immediate vascular assessment 1, 2
• Emergency threshold: A 40 mmHg difference demands immediate vascular imaging to rule out subclavian stenosis, aortic dissection, or large vessel vasculitis 1, 2

Research confirms these recommendations are clinically relevant: studies show that 14.4% of patients have systolic inter-arm differences ≥10 mmHg, and 15.7% have differences that could lead to erroneous clinical decisions if ignored. 3, 4

Subsequent Visit Protocol

Always use the arm with the higher blood pressure reading established at the initial visit for all future measurements. 1 This prevents underdiagnosis of hypertension and ensures consistent monitoring for treatment decisions. 1 Document which arm has the higher reading in the medical record to maintain consistency across visits and providers. 1

Why This Matters

Switching between arms introduces unnecessary variability and may mask true blood pressure changes during treatment monitoring. 2 Using the lower-reading arm consistently would systematically underestimate blood pressure and lead to inadequate treatment. 1, 2

Critical Technical Requirements for Accurate Measurement

Regardless of which arm is used, proper positioning is absolutely essential:

• Arm position: The cuff must be positioned at the exact level of the right atrium (mid-sternum or fourth intercostal space when sitting) 5, 1, 6
• Hydrostatic error: Arm position errors create clinically significant measurement errors of approximately 2 mmHg for every inch above or below heart level, potentially totaling 10 mmHg or more 5, 6, 7
• Arm support: The arm must be supported on a desk or armrest—never have the patient hold their arm up, as isometric muscle contraction raises blood pressure 5, 6
• Cuff size: Use a cuff with a bladder that encircles at least 80% of the arm circumference 1, 6

Special Circumstances

Post-Mastectomy or Lymphedema

• Blood pressure can be measured in either arm unless lymphedema is present, in which case use the contralateral arm 1
• If both arms have lymphedema or arteriovenous fistulas, consider lower extremity measurement, recognizing that leg pressures are typically 10-20 mmHg higher than brachial pressures 1, 2, 6

Lateral Decubitus Position

• Use the non-dependent (upper) arm when the patient is in lateral decubitus position, as this arm can be properly supported and positioned at right atrial level 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 1, 2
• Dismissing large inter-arm differences as normal variation without proper evaluation can miss serious vascular pathology—differences ≥20 mmHg require urgent vascular evaluation 1, 2
• Using different measurement techniques or cuff sizes between arms during the initial bilateral measurement can create artificial differences 2
• Failing to position both arms at heart level during the initial comparison introduces hydrostatic pressure errors that confound the true inter-arm difference 2, 6

High-Risk Populations Requiring Vigilant Bilateral Measurement

Actively measure both arms in patients with: 3

• Age ≥65 years
• Lifestyle-related diseases (diabetes, hyperlipidemia)
• History of vascular events
• Smoking history
• Moderate fever at presentation

These factors are associated with higher likelihood of clinically significant inter-arm differences ≥10 mmHg. 3