How to measure Ankle-Brachial Index (ABI) in a patient with hypertension taking amlodipine (calcium channel blocker) and telmisartan (angiotensin II receptor antagonist) with a history of peripheral edema?

How to Measure the Ankle-Brachial Index (ABI)

Measure the ABI with the patient supine after 5-10 minutes of rest, using a Doppler ultrasound device to obtain systolic pressures from both brachial arteries and both ankle arteries (dorsalis pedis and posterior tibial), then calculate the ratio by dividing the higher ankle pressure by the higher brachial pressure for each leg. 1

Patient Preparation

Position the patient supine with head and heels fully supported for 5-10 minutes before measurement in a room with constant temperature (19°C–22°C or 66°F–72°F). 1, 2 This resting period is critical to ensure accurate baseline measurements and prevent hydrostatic pressure errors. 1

Key preparation requirements:

• Ensure the patient has not smoked for at least 2 hours before measurement, as smoking decreases ankle pressures and affects ABI results 2
• Cover any open wounds with impermeable dressing to prevent contamination 2
• The patient must remain in the supine position throughout the measurement 1

Equipment Required

Use an 8-10 MHz Doppler ultrasound probe with Doppler gel for all measurements. 2 Apply blood pressure cuffs of appropriate size—the cuff width should be at least 40% of the limb circumference. 2 Both oscillometric and Doppler methods have shown good concordance, though Doppler remains the standard. 1

Measurement Sequence

Follow this standardized counterclockwise sequence: 2

1. First arm (right brachial artery) - Place cuff on upper arm and measure systolic pressure
2. First ankle posterior tibial (PT) artery - Place cuff just above the ankle
3. First ankle dorsalis pedis (DP) artery - Same leg, measure DP pressure
4. Other ankle PT artery - Switch to opposite leg
5. Other ankle DP artery - Same leg, measure DP pressure
6. Other arm (left brachial artery) - Complete with second arm measurement

Critical measurement rule: If the systolic blood pressure of the first arm exceeds the second arm by >10 mm Hg, repeat the first arm measurement and disregard the initial reading to ensure accuracy. 2 Average the first and last right arm measurements unless they differ by >10 mm Hg; if the difference exceeds 10 mm Hg, discard the first measurement and use only the second. 2

ABI Calculation

For diagnostic purposes (confirming PAD):

• ABI = Higher ankle pressure (PT or DP) ÷ Higher brachial pressure 1, 2
• This method provides higher specificity (0.99 vs 0.93) and minimizes overdiagnosis in healthy subjects 2, 3

For cardiovascular risk assessment:

• ABI = Lower ankle pressure (PT or DP) ÷ Higher brachial pressure 2, 3
• This method provides higher sensitivity (0.89 vs 0.66) and identifies more individuals at cardiovascular risk 2, 3

Always use the highest brachial systolic pressure from either arm as the denominator. 2

Interpretation of Results

Report ABI results using these standardized categories: 1

• Abnormal (PAD present): ABI ≤0.90 1
• Borderline: ABI 0.91-0.99 1
• Normal: ABI 1.00-1.40 (optimal range 1.11-1.40) 1, 3
• Non-compressible arteries: ABI >1.40 1

The ABI has 68-84% sensitivity and 84-99% specificity for PAD diagnosis. 1

Special Considerations for Your Patient Context

In patients with peripheral edema (like your patient on amlodipine and telmisartan):

• The edema itself does not interfere with ABI measurement, as the Doppler detects arterial flow beneath the tissue 1
• Ensure proper cuff sizing to accommodate any limb swelling—the cuff width must still be at least 40% of limb circumference 2
• Note that amlodipine-induced edema is a venous phenomenon and does not affect arterial pressure measurements 4, 5

Avoid placing the cuff over areas of significant edema if possible, but if unavoidable, the measurement remains valid as long as proper technique is maintained. 1

When Non-Compressible Arteries Are Present (ABI >1.40)

If ABI >1.40, this indicates arterial calcification (common in diabetes and chronic kidney disease), and the ABI cannot reliably diagnose PAD. 1 In this situation, measure the toe-brachial index (TBI) instead: 1

• Apply a small cuff to the base of the great toe or second toe 2
• Use photoplethysmography probe on distal pulp of toe 1
• TBI = Toe systolic pressure ÷ Higher brachial pressure 2
• Abnormal TBI: ≤0.70 1, 2

The TBI has 45-100% sensitivity and 17-100% specificity for PAD diagnosis in patients with non-compressible arteries. 1

Post-Exercise ABI (When Resting ABI is Normal but PAD Suspected)

If the patient has exertional leg pain relieved by rest and a resting ABI >0.90, perform exercise testing with post-exercise ABI measurements. 1

Post-exercise protocol: 1

• Measure bilateral ankle blood pressure 1 minute after cessation of standardized treadmill exercise
• Start with the symptomatic leg
• Simultaneously measure brachial systolic blood pressure
• Positive for PAD: Drop in absolute ankle pressure >30 mm Hg OR drop of >20% in post-exercise ABI 1

Common Pitfalls to Avoid

Critical errors that compromise accuracy:

• Relying on a single measurement when values are borderline (0.91-1.00)—always request repeat measurements for confirmation 2
• Not allowing adequate 5-10 minute rest period before measurement 1, 2
• Using improperly sized cuffs (must be ≥40% of limb circumference) 2
• Measuring in seated position without hydrostatic correction 6
• Failing to use the higher brachial pressure as denominator 2
• Not recognizing non-compressible arteries (ABI >1.40) and proceeding with standard interpretation 1
• Relying solely on palpable pulses to assess arterial circulation instead of objective ABI measurement 3

Training Requirements

Technicians performing ABI should have basic knowledge of vascular anatomy, physiology, and clinical presentation of PAD, understand how a Doppler device functions, and demonstrate reproducible results in both healthy individuals and those with PAD. 2 The procedure requires both didactic and experiential learning with emphasis on correct technique and demonstration of proficiency. 2

Time Efficiency

Automated ABI measurement using oscillometric devices takes approximately 5.8 minutes versus 9.3 minutes for Doppler measurement, with good correlation (r=0.86) and 95% agreement in diagnosing PAD. 7 However, Doppler remains the gold standard for initial diagnostic purposes. 1