What is the normal inter‑extremity blood pressure difference (systolic and diastolic) between arms, between legs, and between an arm and a leg?

Acceptable Blood Pressure Range Between Extremities

Normal inter-arm systolic blood pressure differences are typically 1-3 mmHg, with approximately 20% of healthy individuals showing differences up to 10 mmHg; differences ≥10 mmHg warrant repeat measurement and attention, while differences ≥15-20 mmHg are definitively abnormal and require urgent vascular evaluation. 1, 2, 3

Normal Inter-Arm Blood Pressure Differences

Systolic Blood Pressure

• Mean normal difference: 1-3 mmHg between arms in healthy individuals 1
• Absolute mean difference: approximately 6 mmHg when measured simultaneously 4
• Up to 10 mmHg difference occurs in ~20% of normal individuals and represents the threshold for clinical attention 2, 3, 4
• 83-90% of healthy patients have differences ≤6 mmHg 5

Diastolic Blood Pressure

• Mean normal difference: approximately 1 mmHg between arms 1
• Absolute mean difference: approximately 5 mmHg when measured simultaneously 4
• Differences >10 mmHg occur in only 11% of the population 4
• 92-96% of healthy patients have differences ≤6 mmHg 5

Clinical Thresholds Requiring Action

10 mmHg Threshold (Attention Level)

• Warrants repeat measurement to confirm reproducibility 2, 3
• Found in approximately 20% of normal individuals, so not automatically pathological 2, 4
• Associated with peripheral vascular disease (sensitivity 32%, specificity 91%) 6
• Use the higher-reading arm for all subsequent measurements 3

15-20 mmHg Threshold (Abnormal - Requires Evaluation)

• Definitively abnormal and strongly suggests vascular pathology 3, 6
• Most commonly indicates subclavian or innominate artery stenosis 1, 3
• Associated with 2.5-fold increased risk of peripheral vascular disease 6
• Associated with increased cardiovascular mortality (HR 1.7) and all-cause mortality (HR 1.6) 6
• Requires vascular imaging and thorough examination 1, 3

40 mmHg Threshold (Emergency Evaluation)

• Strongly suggests critical vascular pathology requiring immediate evaluation 1
• Consider aortic dissection, especially with acute symptoms (chest pain, back pain, syncope) 1, 3
• May indicate complete or near-complete arterial occlusion 1

Arm-to-Leg Blood Pressure Differences

Normal Arm-to-Ankle Differences (Supine Position)

• Ankle systolic BP is normally 17 mmHg HIGHER than arm BP (95% CI 15.4-21.3 mmHg) in the general population 7
• Ankle diastolic BP shows no significant difference from arm BP (-0.3 mmHg, 95% CI -1.5 to 1.0 mmHg) 7
• This physiological gradient reflects normal hydrostatic and anatomical factors 7

Pathological Arm-to-Leg Differences

• In patients with vascular disease, ankle SBP may be 33 mmHg LOWER than arm BP (95% CI -59.1 to -7.6 mmHg) 7
• Lower ankle pressures suggest peripheral arterial disease affecting lower extremities 7

Critical Measurement Technique Requirements

Positioning (Most Common Source of Error)

• Both arms must be positioned at heart level (mid-sternum/fourth intercostal space) 1, 2, 3
• Arm position errors create artificial differences of 10 mmHg or more (2 mmHg for every inch above or below heart level) 1, 2
• Arms must be fully supported; having patients hold their arms up causes isometric contraction that falsely elevates pressure 1, 3

Cuff Selection

• Use appropriately sized cuffs for each arm based on circumference 1, 3
• Using different cuff sizes between arms creates false differences 1, 3
• Undersized cuffs can produce unrecordable or falsely elevated readings 1

Measurement Protocol

• Measure both arms at the initial visit 3
• Take three measurements per arm, 1-2 minutes apart, after 5 minutes of seated rest 1
• If difference >10 mmHg detected, remeasure the original arm to confirm consistency 1
• Sequential measurements are acceptable if done properly, though simultaneous is ideal 1

Pathological Causes of Abnormal Differences

Subclavian/Innominate Artery Stenosis

• Most common cause of differences ≥15-20 mmHg 1, 3, 6
• Creates pressure gradient across narrowed vessel, resulting in lower distal pressure 1
• Mean difference with proven stenosis (>50% occlusion): 37 mmHg 6
• Patients with peripheral artery disease have substantially increased risk 1

Aortic Dissection

• Difference ≥20 mmHg combined with acute chest pain, back pain, syncope, or neurological symptoms constitutes a medical emergency 1, 3
• Requires immediate CT or MR angiography 1

Other Vascular Pathology

• Aortic coarctation (particularly in younger patients) 1, 3
• Takayasu arteritis or large vessel vasculitis 1
• Complete arterial occlusion (unrecordable pressure in one arm) 1

Management Algorithm

For Differences 10-14 mmHg

• Confirm with repeat measurements using proper technique 2, 3
• Use higher-reading arm for all future measurements 3
• Consider vascular risk factor assessment 6, 8

For Differences ≥15-20 mmHg

• Confirm with repeat simultaneous bilateral measurements 3
• Perform thorough vascular examination: palpate pulses, auscultate for bruits, assess for peripheral vascular disease signs 1, 3
• Order duplex ultrasound of subclavian and axillary arteries 1
• Consider CT or MR angiography if aortic pathology suspected 1, 3
• Refer to vascular surgery or cardiology 1
• Always use the higher-reading arm for hypertension diagnosis and management 1, 3

For Unrecordable Pressure in One Arm

• Verify proper cuff size and technique first 1
• Assume complete or near-complete arterial occlusion until proven otherwise 1
• Urgent vascular imaging required to exclude critical obstruction, dissection, or vasculitis 1
• Palpate pulses and assess for limb ischemia 1

Critical Pitfalls to Avoid

• Never dismiss differences ≥20 mmHg as normal variation or measurement error without proper evaluation—this can miss life-threatening conditions like aortic dissection 1, 2, 3
• Do not use different cuff sizes or measurement techniques between arms during confirmation 1, 3
• Failing to position both arms at heart level is the most common technical error, creating false 10+ mmHg differences 1, 2
• Do not measure BP in arms with arteriovenous fistulas or after axillary lymph node dissection, as this creates artificial differences 1
• Always use the higher-reading arm for ongoing monitoring to avoid underestimating BP and undertreating hypertension 1, 3
• Do not overlook the need for cardiac evaluation in patients with subclavian disease, as they frequently have concomitant coronary artery disease 1