What is the current workup for peripheral arterial disease (PAD)?

Current Workup for Peripheral Arterial Disease

The ankle-brachial index (ABI) is the first-line diagnostic test for PAD, recommended for all patients aged ≥65 years or aged 50-64 years with smoking history or diabetes, with an ABI ≤0.90 confirming the diagnosis. 1

Initial Clinical Assessment

Patient History and Risk Factor Identification

• Assess for exertional leg symptoms, nonhealing wounds, and walking impairment 1
• Document smoking history (present in >80% of PAD patients and increases risk 2-6 fold) 2
• Identify diabetes mellitus (increases PAD risk 2-4 fold) 1, 2
• Evaluate for coronary artery disease, as PAD and CAD frequently coexist due to shared atherosclerotic pathophysiology 2
• Note that classic claudication occurs in only 11% of PAD patients, so absence of typical symptoms does not exclude disease 3

Physical Examination

• Perform comprehensive pulse examination of both lower extremities (femoral, popliteal, dorsalis pedis, posterior tibial) 1, 4
• Inspect feet for ulcers, gangrene, or tissue loss 1
• Measure blood pressure in both arms to identify subclavian artery stenosis (difference >15-20 mmHg is significant) 4
• Assess for neuropathy in diabetic patients, as this increases risk of foot ulceration 2

Diagnostic Testing Algorithm

First-Line: Ankle-Brachial Index (ABI)

• Measure ABI in both legs for all suspected PAD patients 1
• ABI ≤0.90 confirms PAD diagnosis (sensitivity 79-95%, specificity 95-100%) 1, 5
• ABI 0.91-0.99 is borderline and warrants close follow-up 1
• ABI 1.00-1.40 is normal 1
• ABI >1.40 indicates non-compressible vessels (medial arterial calcification) 1

When ABI is Non-Diagnostic or Unreliable

For non-compressible vessels (ABI >1.40):

• Obtain toe-brachial index (TBI), as digital arteries are rarely affected by medial calcification 1
• TBI <0.70 confirms PAD diagnosis 1
• This scenario is particularly common in patients with long-standing diabetes or advanced age 1

For normal ABI with persistent clinical suspicion:

• Perform post-exercise ABI (measured 1 minute after standardized treadmill exercise) 1, 4
• A fall in absolute ankle BP >30 mmHg is diagnostic 1
• Note that a post-exercise ABI drop >20% has high false-positive rates in healthy populations and should be interpreted cautiously 1

Supplementary Non-Invasive Tests

Duplex ultrasound (DUS):

• Recommended as first-line imaging for PAD screening and anatomic localization 1
• Provides dynamic, non-invasive, radiation-free examination with 88% sensitivity and 95% specificity for >50% stenosis 1
• Localizes vascular lesions and quantifies severity through velocity criteria 1
• Distinguishes atherosclerotic from non-atherosclerotic lesions 1
• Caveat: Reliability depends heavily on sonographer expertise 1

Segmental pressure measurements:

• Useful when anatomic localization is required for treatment planning 1
• Helps determine level of arterial obstruction 1

Transcutaneous oxygen pressure (TcPO2):

• Indicated for evaluating tissue viability in chronic limb-threatening ischemia (CLTI) 1
• Resting TcPO2 >30 mmHg predicts favorable wound healing 1
• Resting TcPO2 <10 mmHg associated with poor prognosis for healing and amputation 1
• Caveat: Values affected by skin thickness, probe temperature, inflammation, and edema 1

Advanced Imaging for Revascularization Planning

Cross-sectional imaging is advisable when revascularization is being considered 1:

• ECG-triggered cardiovascular computed tomography (CCT) for comprehensive aortic and lower extremity assessment 1
• Cardiovascular magnetic resonance (CMR) when chronic follow-up is required to minimize radiation exposure 1
• These modalities provide detailed anatomic information beyond what DUS can offer 1

Laboratory Evaluation

Comprehensive cardiovascular risk factor assessment is recommended 1:

• Lipid panel (for statin therapy guidance)
• Hemoglobin A1c (in diabetic patients)
• Renal function (affects contrast imaging decisions and medication choices)
• Complete blood count

Special Populations

Diabetic patients:

• ABI accuracy is lower due to arterial calcification 1
• TBI should be obtained if ABI >1.40 1
• Annual screening recommended once diabetes is diagnosed 1
• Assess for neuropathy, which compounds amputation risk 7-15 fold 2

Patients with critical limb-threatening ischemia:

• Expedited evaluation required 1, 4
• Use WIfI (Wound, Ischemia, foot Infection) classification to stratify amputation risk 1
• Early referral to vascular team essential for limb salvage 4

Common Pitfalls to Avoid

• Do not rely solely on symptoms: Only 11% of PAD patients have classic claudication 3
• Do not accept ABI >1.40 as normal: This indicates non-compressible vessels requiring TBI 1
• Do not use post-exercise ABI drop >20% alone: High false-positive rate in healthy populations 1
• Do not delay imaging in CLTI: These patients require urgent vascular team evaluation 4
• Do not forget bilateral measurements: ABI should be measured in both legs to establish baseline 1

Screening Recommendations

The 2024 ESC Guidelines recommend ABI screening for 1:

• All men aged ≥65 years with smoking history (Class I, Level A)
• First-degree relatives of AAA patients aged ≥50 years (Class I, Level C)

The 2024 ACC/AHA Guidelines recommend screening for 1:

• Patients aged ≥65 years
• Patients aged 50-64 years with diabetes or smoking history
• Patients with exertional leg symptoms or nonhealing wounds

The American Diabetes Association recommends ABI screening for diabetic patients >50 years 5, though the U.S. Preventive Services Task Force does not recommend population-based screening due to lack of evidence that screening reduces cardiovascular events 5.