Ankle-Brachial Index Test Protocol

Standardized ABI Protocol

• The American Heart Association recommends that the ABI should be performed by qualified individuals, including physicians, nurses, vascular technicians, and other allied health professionals who have received proper training in the procedure, with training including both didactic and experiential learning, and emphasis on correct technique and demonstration of proficiency 1, 2
• The American Heart Association recommends a standardized sequence for limb pressure measurement: first arm, first posterior tibial (PT) artery, first dorsalis pedis (DP) artery, other PT artery, other DP artery, and other arm 1
• If the systolic blood pressure (SBP) of the first arm exceeds the SBP of the other arm by >10 mm Hg, the blood pressure of the first arm should be repeated, and the first measurement disregarded, to ensure accurate results 1, 3

Training Requirements for Technicians

• Technicians performing the ABI should have basic knowledge of vascular anatomy, physiology, and the clinical presentation of peripheral arterial disease (PAD), and understand how a Doppler device functions, with the ability to demonstrate reproducible results in both healthy individuals and those with PAD 1, 2, 4

Diagnostic Considerations

• For diagnostic purposes, using the higher ankle pressure to calculate the ABI improves specificity (0.99 vs 0.93) 3
• For cardiovascular risk assessment, using the lower ankle pressure identifies more individuals at risk (sensitivity 0.89 vs 0.66) 3

Common Pitfalls to Avoid

• Relying solely on a single measurement when values are borderline (0.91-1.00) rather than requesting repeat measurements for confirmation is a common pitfall, and the American Heart Association recommends repeat measurements in such cases 2

Measuring the Ankle-Brachial Index (ABI)

Patient Preparation and Equipment

• The American Heart Association recommends measuring the Ankle-Brachial Index (ABI) using a Doppler ultrasound device with the patient in a supine position after 5-10 minutes of rest, following a standardized protocol that includes measuring systolic pressures in both arms and ankles, then calculating the ratio of ankle to arm pressure 5, 6, 7
• Position the patient supine with head and heels fully supported for 5-10 minutes before measurement in a room with comfortable temperature (19°C–22°C/66°F–72°F) 5, 6
• Ensure the patient has not smoked for at least 2 hours before the measurement, as smoking can decrease ankle pressures and affect ABI results 8, 9
• Cover any open wounds with impermeable dressing to prevent contamination 5, 6

Equipment and Measurement Procedure

• Use an 8-10 MHz Doppler ultrasound probe and Doppler gel for measurements 5, 6
• Apply blood pressure cuffs of appropriate size (width should be at least 40% of limb circumference) 8, 9
• Measure both arms and use the highest reading as the denominator for ABI calculation 6, 7
• For diagnostic purposes, ABI = Higher ankle pressure (PT or DP) / Higher brachial pressure 10

Interpretation of Results

• Normal ABI: 0.91-1.40 (optimal range: 1.11-1.40) 11
• Abnormal (indicating PAD): ≤0.90 11
• Non-compressible arteries: >1.40 (suggests arterial calcification) 11

Special Considerations

• Avoid placing cuff over recent bypass grafts due to risk of thrombosis 8, 9
• In patients with clinical suspicion of PAD but normal resting ABI, consider post-exercise ABI measurement 11
• Serial measurements provide more accurate assessment than a single measurement 11

Ankle-Brachial Index and Toe-Brachial Index Measurement Guidelines

Patient Preparation and Measurement

• The European Heart Journal recommends that both ABI and TBI should be performed in a supine position after 5-10 minutes of rest in a room with constant temperature, using standardized protocols to ensure accurate diagnosis of peripheral arterial disease 12, 13
• The American College of Cardiology suggests applying an appropriately sized cuff to the upper arm for brachial pressure measurement 13
• The European Heart Journal recommends measuring brachial pressures as described above, and then applying a small cuff to the base of the great toe or second toe for TBI measurement 12

ABI and TBI Calculation and Interpretation

• The American College of Cardiology recommends calculating ABI as the higher ankle pressure (PT or DP) divided by the higher brachial pressure for diagnostic purposes 14
• The European Heart Journal suggests calculating TBI as the toe systolic pressure divided by the higher brachial systolic pressure 12
• The American College of Cardiology and the European Heart Journal recommend the following ABI values: normal (0.91-1.40), borderline (0.90-1.00), abnormal (≤0.90), and non-compressible arteries (>1.40) 12, 13, 14
• The European Heart Journal recommends the following TBI values: normal (>0.70) and abnormal (≤0.70) 12, 13

Special Considerations and Adjunctive Tests

• The American College of Cardiology notes that ABI has 68-84% sensitivity and 84-99% specificity for PAD diagnosis, but reduced sensitivity in patients with diabetes or end-stage chronic kidney disease due to arterial calcification 12, 13, 15
• The European Heart Journal recommends considering alternative tests, such as TBI, when ABI >1.40 with clinical suspicion of PAD 12, 13, 15
• The American College of Cardiology suggests using duplex ultrasound, which provides anatomic and hemodynamic information with 85-90% sensitivity and >95% specificity for stenosis >50% 15

Ankle-Brachial Index Calculation and Interpretation

Basic Principles

• The American Heart Association recommends calculating the Ankle-Brachial Index (ABI) by dividing the ankle systolic pressure by the highest brachial systolic pressure, with the choice of which ankle pressure to use depending on the clinical purpose, to maximize specificity for diagnostic confirmation of Peripheral Artery Disease (PAD) or sensitivity for cardiovascular risk assessment 16, 17

Measurement Protocol

• The American College of Cardiology recommends following a standardized counterclockwise sequence for measuring ABI, including right arm, right posterior tibial artery, right dorsalis pedis artery, left posterior tibial artery, left dorsalis pedis artery, and left arm, to ensure accurate and reliable results 16, 17, 18
• The guideline suggests averaging the first and last right arm measurements unless they differ by >10 mm Hg, and if the difference exceeds 10 mm Hg, discarding the first measurement and using only the second, to minimize errors in ABI calculation 16, 17

Determining the Numerator and Denominator

• For diagnostic purposes, the American Heart Association recommends using the higher of the two ankle pressures (posterior tibial or dorsalis pedis) as the numerator to provide higher specificity (0.99 vs. 0.93) and minimize overdiagnosis in healthy subjects 16, 17, 18
• For cardiovascular risk assessment, the guideline suggests using the lower of the two ankle pressures as the numerator to provide higher sensitivity (0.89 vs. 0.66) and identify more individuals at cardiovascular risk 16, 17, 18
• The American College of Cardiology recommends always using the highest brachial systolic pressure from either arm as the denominator to ensure accurate ABI calculation 16, 17

Interpretation of ABI Values

• An ABI value of ≤0.90 indicates abnormal results and suggests the presence of PAD, according to the American Heart Association 16, 17, 18
• If an ankle artery signal is absent but the other ankle artery shows normal ABI, the guideline recommends performing duplex ultrasound to determine if PAD is present 16, 17, 18

In‑Office Ankle‑Brachial Index (ABI) Testing for Peripheral Arterial Disease

Indications and Recommendations

• The American Heart Association recommends that the ABI be used as the first‑line non‑invasive test for diagnosing peripheral arterial disease (PAD) when clinical suspicion is present (Class I, Level A evidence)【19】【20】.

Qualified Personnel and Training

• The ABI may be performed by qualified health‑care professionals—including physicians, nurses, vascular technicians, and other allied staff—provided they have completed appropriate training, according to the American Heart Association【19】【20】.
• Training programs should combine didactic instruction (vascular anatomy, PAD clinical presentation, Doppler device principles) with hands‑on experiential learning【19】【20】.
• Trainees must demonstrate independent, reproducible performance of each testing step in both healthy individuals and patients with PAD, and must calculate and interpret the ABI correctly【19】【20】.

Technical Procedure

• Prior to measurement, the patient should be positioned supine for at least 10 minutes to allow hemodynamic stabilization【19】.

Interpretation of Results

• These interpretation thresholds and corresponding actions are endorsed by the American Heart Association【19】【20】.