How is the ankle‑brachial pressure index (ABPI) measured?

How to Measure the Ankle-Brachial Pressure Index (ABPI)

The American Heart Association recommends measuring ABPI using a handheld Doppler ultrasound device with the patient supine after 5-10 minutes of rest, following a standardized counterclockwise sequence: right brachial artery, right posterior tibial artery, right dorsalis pedis artery, left posterior tibial artery, left dorsalis pedis artery, and left brachial artery. 1

Patient Preparation

Before beginning the measurement:

• Position the patient supine with head and heels fully supported for 5-10 minutes to allow hemodynamic stabilization 2, 1
• Ensure the room temperature is comfortable (19°C–22°C or 66°F–72°F) 2
• Confirm the patient has not smoked for at least 2 hours before measurement, as smoking decreases ankle pressures and affects ABPI results 3
• Cover any open wounds with impermeable dressing to prevent contamination 2, 3
• Ensure the patient remains still during measurement; if tremor or movement is present, consider alternative methods 2

Equipment Required

• 8-10 MHz handheld Doppler ultrasound probe 2, 3
• Doppler gel 2
• Blood pressure cuffs of appropriate size (width should be at least 40% of limb circumference) 2, 3
• Avoid placing cuffs over recent bypass grafts due to thrombosis risk 3

Measurement Sequence

Follow this standardized counterclockwise sequence: 1, 3

1. Right brachial artery (first arm)
2. Right posterior tibial artery
3. Right dorsalis pedis artery
4. Left posterior tibial artery
5. Left dorsalis pedis artery
6. Left brachial artery (second arm)

Critical Rule for Arm Measurements:

• If the first arm SBP exceeds the second arm SBP by >10 mm Hg, repeat the first arm measurement and disregard the initial reading 3
• Suspect subclavian artery stenosis when the interarm SBP difference is ≥15 mm Hg 2

Technique for Each Measurement

For ankle measurements:

• Place the cuff around the ankle with the lower edge 2 cm above the superior aspect of the medial malleolus 2
• Apply Doppler gel over the sensor 2
• Position the probe at a 45° to 60° angle to the skin surface in the area of the pulse 2
• Move the probe until the clearest signal is heard 2
• Inflate the cuff progressively to 20 mm Hg above the level where the flow signal disappears (maximum 300 mm Hg) 2
• Deflate slowly and record the pressure at which the flow signal reappears 2

Calculation Methods

The calculation method depends on your clinical purpose:

For Diagnostic Purposes (Confirming PAD):

ABPI = Higher ankle pressure (PT or DP) ÷ Higher brachial pressure 1, 3

• This method provides higher specificity (99% vs 93%) and minimizes overdiagnosis 1
• Use the highest brachial SBP from either arm as the denominator 3

For Cardiovascular Risk Assessment:

ABPI = Lower ankle pressure (PT or DP) ÷ Higher brachial pressure 1, 3

• This method provides higher sensitivity (89% vs 66%) and identifies more at-risk individuals 1

Interpretation of Results

Report ABPI values to 2 decimal places using these categories: 1

ABPI Value	Interpretation	Clinical Action
≤0.90	PAD confirmed	Initiate cardiovascular risk reduction; consider vascular referral if symptomatic [1,4]
0.91-0.99	Borderline	Perform exercise ABPI or toe-brachial index [1,4]
1.00-1.40	Normal	Standard cardiovascular risk management [1,4]
>1.40	Non-compressible arteries	ABI invalid; measure toe-brachial index [1,4]

Special Considerations

In Diabetic Patients:

• ABPI >1.40 is common due to medial arterial calcification 1
• Always measure toe-brachial index (TBI) when ABPI >1.40 1, 4
• TBI ≥0.75 reliably excludes PAD; TBI <0.70 indicates PAD 1

When Clinical Suspicion Persists Despite Normal Resting ABPI:

• Perform post-exercise ABPI; a drop of ≥0.15 indicates at least moderate arterial occlusive disease 4

Reliability Considerations:

• Doppler method is the most reliable compared to palpation or oscillometric methods 2
• Serial measurements provide more accurate assessment than a single measurement 3, 4
• Reproducibility is higher when performed by skilled, trained examiners 2

Common Pitfalls to Avoid

• Do not rely on a single measurement when values are borderline (0.91-1.00); request repeat measurements 3
• Do not apply compression therapy when ABPI <0.50 (absolute contraindication due to tissue damage risk) 4
• Do not trust ABPI alone in diabetic patients or those with chronic kidney disease; arterial calcification produces falsely elevated values 4
• Do not place cuffs over distal bypass grafts (thrombosis risk) or directly over ulcers 2, 3

Training Requirements

Personnel performing ABPI should: 3

• Have basic knowledge of vascular anatomy, physiology, and PAD clinical presentation
• Understand Doppler device function
• Complete both didactic and hands-on experiential training
• Demonstrate reproducible results in both healthy individuals and PAD patients before performing independently