What is the procedure for performing an Ankle-Brachial Pressure Index (ABPI) test on a patient?

How to Perform an Ankle-Brachial Pressure Index (ABPI)

The American Heart Association recommends measuring the ABPI using a handheld Doppler ultrasound device with the patient supine after 5-10 minutes of rest, following a standardized counterclockwise sequence: right arm, right posterior tibial (PT), right dorsalis pedis (DP), left PT, left DP, left arm, then repeating the first arm measurement. 1, 2

Patient Preparation

• Position the patient supine with head and heels fully supported for 5-10 minutes before measurement in a room temperature of 19°C–22°C (66°F–72°F) 1
• Ensure the patient has not smoked for at least 2 hours before measurement, as smoking decreases ankle pressures and affects ABPI results 1, 2
• Cover any open wounds with impermeable dressing to prevent contamination 1, 2
• Ensure the patient remains still during pressure measurements; if unable (e.g., tremor), consider alternative methods 1

Equipment Setup

• Use an 8-10 MHz handheld Doppler ultrasound probe with Doppler gel 1
• Select appropriately sized blood pressure cuffs with width covering at least 40% of limb circumference 1, 2
• Critical: Do not place cuffs over recent bypass grafts due to thrombosis risk 1, 2
• For ankle measurements, place the lower edge of the cuff 2 cm above the superior aspect of the medial malleolus using straight wrapping method 1

Measurement Technique

Doppler Probe Positioning

• Apply Doppler gel over the sensor 1
• Place the probe at a 45° to 60° angle to the skin surface in the area of the pulse 1
• Move the probe around until the clearest signal is heard 1

Pressure Measurement Protocol

• Inflate the cuff progressively up to 20 mm Hg above the level where the flow signal disappears 1
• Deflate slowly to detect the pressure level where the flow signal reappears 1
• Maximum inflation is 300 mm Hg; if flow is still detected, deflate rapidly to avoid pain 1

Standardized Measurement Sequence

Follow this exact counterclockwise sequence: 1, 2

1. Right brachial artery (arm)
2. Right posterior tibial artery (ankle)
3. Right dorsalis pedis artery (ankle)
4. Left posterior tibial artery (ankle)
5. Left dorsalis pedis artery (ankle)
6. Left brachial artery (arm)
7. Repeat right brachial artery measurement

Handling the Repeated First Arm Measurement

• Average the first and last right arm measurements unless they differ by >10 mm Hg 1, 2
• If the difference exceeds 10 mm Hg, discard the first measurement and use only the second 1, 2
• This approach minimizes the white coat effect 1

Calculating the ABPI

Determining the Denominator

• Always use the highest brachial systolic pressure from either arm as the denominator 1, 2, 3
• If the systolic blood pressure difference between arms exceeds 15 mm Hg, suspect subclavian artery stenosis (100% sensitivity and specificity) 1

Determining the Numerator (Purpose-Dependent)

For diagnostic purposes (confirming PAD): 2, 3

• Use the higher of the two ankle pressures (PT or DP) from each leg
• This provides higher specificity (0.99 vs 0.93) and minimizes overdiagnosis 2
• Formula: ABPI = Higher ankle pressure (PT or DP) / Highest brachial pressure

For cardiovascular risk assessment: 2, 3

• Use the lower of the two ankle pressures (PT or DP) from each leg
• This provides higher sensitivity (0.89 vs 0.66) and identifies more at-risk individuals 2

Interpreting ABPI Values

• Normal: 0.91-1.40 (optimal range: 1.11-1.40) 1, 2, 4
• Borderline: 0.90-1.00 (interpret with clinical context; consider repeat measurements) 1, 2, 4
• Abnormal (PAD): ≤0.90 1, 2, 4
• Non-compressible arteries: >1.40 (suggests arterial calcification; consider toe-brachial index) 1, 2, 4

Critical Pitfalls to Avoid

• Do not rely on a single measurement when values are borderline (0.91-1.00) - request repeat measurements for confirmation 2
• Do not place cuffs over recent bypass grafts - risk of thrombosis 1, 2
• Do not assume normal ABPI excludes PAD in symptomatic patients - consider post-exercise ABPI if clinical suspicion remains 1, 2
• Do not use compression therapy if ABPI <0.50 - absolute contraindication due to tissue damage risk 4
• Do not ignore ABPI >1.40 with clinical suspicion of PAD - perform toe-brachial index or duplex ultrasound 1, 2

Special Considerations

• In patients with diabetes or end-stage renal disease, arterial calcification may produce falsely elevated ABPI (>1.40), masking true PAD 1, 4
• If ankle artery signal is absent but the other ankle artery shows normal ABPI, perform duplex ultrasound to determine if PAD is present 2
• Serial measurements provide more accurate assessment than a single measurement 2
• The confidence interval for ABPI improves with multiple measurements (reduced by the square root of the number of measurements) 1