How to order Ankle-Brachial Index (ABI) for a patient with claudication

How to Order ABI for a Patient with Claudication

For a patient with claudication symptoms, order a resting ABI immediately as the first-line diagnostic test, and if the resting ABI is normal (0.91-1.30) or borderline (0.91-0.99), proceed directly to exercise ABI testing to confirm the diagnosis. 1

Initial Diagnostic Approach

Resting ABI Measurement

• Order a resting ABI with or without segmental pressures and waveforms as the initial diagnostic test for any patient presenting with exertional leg symptoms consistent with claudication 1
• The ABI is calculated by dividing the higher ankle pressure (dorsalis pedis or posterior tibial) by the higher arm pressure (right or left brachial) 1
• Measure blood pressure in both arms to identify the highest systolic pressure, which is required for accurate ABI calculation 1

Interpretation of Resting ABI Results

Report results using the following categories 1:

• Abnormal: ABI ≤0.90 (confirms PAD diagnosis)
• Borderline: ABI 0.91-0.99 (proceed to exercise testing)
• Normal: ABI 1.00-1.40 (proceed to exercise testing if symptoms persist)
• Noncompressible: ABI >1.40 (order toe-brachial index instead)

Critical Next Step: Exercise ABI Testing

When to Order Exercise Testing

If the resting ABI is normal or borderline in a patient with classic claudication symptoms, immediately order exercise treadmill ABI testing (Class I recommendation, Level of Evidence B) 1

This is essential because:

• Nearly half (46%) of symptomatic patients referred for PAD evaluation have normal resting ABI values 2
• Among patients with normal resting ABI who undergo exercise testing, 31% demonstrate a significant drop in ABI post-exercise, confirming PAD 2
• Exercise ABI objectively measures functional limitations and establishes the diagnosis when resting values are misleading 1

Exercise Testing Protocol

• Perform standard treadmill exercise (typically 2 mph at 12% grade) until moderate-to-maximum claudication occurs 1
• Measure ABI immediately post-exercise 1
• A post-exercise ABI <0.90 or a decrease >20% from baseline confirms PAD 2

Special Circumstances Requiring Alternative Testing

Noncompressible Vessels (ABI >1.40)

• This occurs in approximately 14% of patients, particularly those with diabetes or advanced age 2, 3
• Order toe-brachial index (TBI) as the primary diagnostic test when vessels are noncompressible 1
• Consider pulse volume recordings (PVR) as an adjunctive test 1, 2

When Resting and Exercise ABI Are Both Normal

If symptoms strongly suggest vascular claudication but both resting and exercise ABI are normal, order alternative diagnostic studies 1:

• Toe-brachial index
• Segmental pressure examination with pulse volume recordings
• Duplex ultrasound of lower extremities

Do not proceed to arterial imaging (CTA, MRA, or angiography) if the post-exercise ABI is normal, unless you suspect alternative diagnoses like popliteal entrapment syndrome or isolated internal iliac artery disease 1

Common Pitfalls to Avoid

False-Negative Resting ABI

Be aware that resting ABI has significant limitations in certain populations 3:

• Diabetes mellitus increases the odds of false-negative results by 4.36-fold 3
• Distal lesions (below-knee disease) increase false-negative odds by 3.41-fold 3
• Elderly patients have 3.02-fold increased odds of false-negative results 3
• Overall sensitivity of resting ABI in symptomatic patients is only 61%, though specificity is 87% 3

In these high-risk populations, maintain a low threshold for proceeding directly to exercise ABI testing even with borderline-normal resting values 2, 3

Inadequate Evaluation

• Never rely solely on resting ABI in symptomatic patients—approximately one-third of patients with normal resting ABI will have abnormal exercise ABI 2
• Patients with symptoms of PAD should receive complete vascular laboratory evaluation, not just office-based resting ABI 2

Practical Ordering Algorithm

1. Order resting ABI bilaterally with segmental pressures 1
2. If ABI ≤0.90: Diagnosis confirmed, proceed to treatment planning 1
3. If ABI 0.91-1.40: Order exercise ABI testing 1
4. If ABI >1.40: Order toe-brachial index 1
5. If exercise ABI remains normal but symptoms persist: Consider duplex ultrasound or alternative diagnoses (lumbar spinal stenosis, chronic compartment syndrome) 1, 4

Documentation for Ordering

Specify on the order:

• Bilateral resting ABI with segmental pressures and waveforms
• If resting ABI is normal/borderline: add exercise ABI testing
• Clinical indication: "Intermittent claudication, rule out peripheral arterial disease"

This approach ensures comprehensive evaluation while avoiding unnecessary advanced imaging in patients without confirmed PAD 1, 4.