What is the procedure for performing an ankle brachial index (ABI) test to diagnose peripheral artery disease (PAD)?

How to Perform the Ankle-Brachial Index (ABI)

The ABI should be measured using a standardized protocol: position the patient supine for 5-10 minutes, then measure systolic pressures in sequence (first arm, first posterior tibial artery, first dorsalis pedis artery, other posterior tibial artery, other dorsalis pedis artery, other arm) using a blood pressure cuff and Doppler device, calculating the ratio of the higher ankle pressure to the higher brachial pressure. 1, 2

Patient Preparation

Before measurement:

• Position the patient supine with head and heels fully supported 2
• Allow 5-10 minutes of rest in a room temperature of 19°C–22°C (66°F–72°F) 2
• Ensure the patient has not smoked for at least 2 hours, as smoking decreases ankle pressures 2
• Cover any open wounds with impermeable dressing 2

Equipment Required

• Blood pressure cuffs of appropriate size (width should be at least 40% of limb circumference) 2
• 8-10 MHz Doppler ultrasound probe 2
• Doppler gel 2
• Sphygmomanometer (manual or aneroid) 1

Standardized Measurement Sequence

Follow this exact counterclockwise sequence: 1, 2

1. First arm (right brachial artery)
2. First posterior tibial (PT) artery (right ankle)
3. First dorsalis pedis (DP) artery (right ankle)
4. Other posterior tibial artery (left ankle)
5. Other dorsalis pedis artery (left ankle)
6. Other arm (left brachial artery)

Critical adjustment: If the systolic blood pressure of the first arm exceeds the second arm by >10 mm Hg, repeat the first arm measurement and discard the initial reading 1, 2

Measurement Technique

For each artery:

• Apply appropriately sized blood pressure cuff above the measurement site 2
• Apply Doppler gel and locate the arterial signal with the Doppler probe 2
• Inflate the cuff until the signal disappears 1
• Slowly deflate the cuff and record the pressure when the signal returns (systolic pressure) 1
• Measure both posterior tibial and dorsalis pedis arteries at each ankle 1

ABI Calculation

The calculation method depends on your clinical purpose: 1, 2

For Diagnostic Purposes (Confirming PAD):

• Numerator: Use the higher of the two ankle pressures (PT or DP) from each leg 1, 2
• Denominator: Use the higher brachial pressure from either arm 1, 2
• This method provides higher specificity (0.99 vs 0.93) and minimizes overdiagnosis 2

For Cardiovascular Risk Assessment:

• Numerator: Use the lower of the two ankle pressures (PT or DP) from each leg 1
• Denominator: Use the higher brachial pressure from either arm 1
• This method provides higher sensitivity (0.89 vs 0.66) and identifies more at-risk individuals 2

Calculate ABI for each leg separately and use the lower ABI of the two legs to identify more individuals at risk of cardiovascular events. 1

Interpretation of Results

ABI values: 1

• Normal: 0.91-1.40 (optimal range: 1.11-1.40) 2
• Borderline: 0.91-1.00 (warrants further evaluation) 1
• Abnormal (PAD confirmed): ≤0.90 1
• Non-compressible arteries: >1.40 (suggests arterial calcification) 1

Critical Pitfalls to Avoid

Common errors that compromise accuracy:

• Inadequate rest period: Measuring immediately without 5-10 minutes of supine rest produces inaccurate results 2
• Wrong calculation method: Using the lower ankle pressure for diagnosis reduces specificity from 0.99 to 0.93 2
• Ignoring arm pressure discrepancy: Failing to remeasure when arm pressures differ by >10 mm Hg introduces systematic error 1
• Single measurement in borderline cases: When ABI is 0.91-1.00, repeat measurements are essential for confirmation 2
• Inappropriate cuff size: Cuff width <40% of limb circumference yields inaccurate pressures 2
• Placing cuff over recent bypass grafts: This risks thrombosis 2

When ABI is Unreliable

If ABI >1.40 (non-compressible arteries):

• Proceed immediately to toe-brachial index (TBI) measurement 1
• This occurs commonly in diabetes and chronic kidney disease due to medial arterial calcification 1, 3
• Normal TBI: >0.70; Abnormal TBI: ≤0.70 1, 4

If ABI is 0.91-1.40 but clinical suspicion remains high:

• Perform post-exercise ABI testing 1
• A post-exercise ankle pressure decrease >30 mm Hg or ABI decrease >20% confirms PAD 1

Training Requirements

Personnel performing ABI must: 1, 2

• Include physicians, nurses, vascular technicians, or allied health professionals 1
• Receive both didactic and experiential training 1, 2
• Understand vascular anatomy, physiology, and PAD clinical presentation 2
• Demonstrate reproducible results in both healthy individuals and those with PAD 2

Time Required

The complete ABI measurement takes approximately 8 minutes when performed correctly 5