What is the role of Ankle-Brachial Index (ABI) testing in diagnosing Peripheral Artery Disease (PAD)?

Role of Ankle-Brachial Index (ABI) Testing in Diagnosing Peripheral Artery Disease

ABI is the first-line noninvasive diagnostic test for PAD and should be performed in any patient with exertional leg symptoms, claudication, walking impairment, ischemic rest pain, nonhealing wounds, absent pulses, or femoral bruits. 1

Diagnostic Performance

ABI demonstrates excellent diagnostic accuracy for detecting significant PAD:

• Sensitivity ranges from 68-84% and specificity from 84-99% when using the Doppler method, with areas under the ROC curve of 0.87-0.95 for detecting significant stenosis 1, 2
• The test shows high accuracy (72.1-89.2%) for identifying ≥50% stenosis, though sensitivity can be lower in elderly patients and those with diabetes 3
• The pooled diagnostic odds ratio is 15.33, with positive likelihood ratio of 4.18 and negative likelihood ratio of 0.29 4

Who Should Be Tested

Symptomatic Patients (Test Immediately)

• Any patient with exertional leg symptoms, claudication, or walking impairment 1
• Patients with ischemic rest pain or nonhealing wounds 1
• Those with absent pulses or femoral bruits on examination 1

Asymptomatic Screening Candidates

• Age ≥65 years 1
• Age 50-64 years with atherosclerotic risk factors (smoking, diabetes, hypertension, hyperlipidemia) or family history of PAD 1
• Age <50 years with diabetes plus one additional atherosclerotic risk factor 1
• Known atherosclerotic disease in another vascular bed (coronary or cerebrovascular) 1

Proper Measurement Technique

The patient must be supine for at least 5 minutes before measurement to ensure accurate readings 1, 5

Measurement Sequence

1. First arm systolic blood pressure 5
2. First posterior tibial artery 5
3. First dorsalis pedis artery 5
4. Other posterior tibial artery 5
5. Other dorsalis pedis artery 5
6. Other arm 5

• If the first arm exceeds the other by >10 mmHg, repeat the first arm measurement and disregard the initial reading 5
• Calculate ABI by dividing the highest ankle pressure (either posterior tibial or dorsalis pedis) by the highest brachial pressure 1, 5

Interpretation of Results

• ABI ≤0.90: Abnormal—confirms PAD diagnosis 1, 5, 2
• ABI 0.91-0.99: Borderline—warrants further cardiovascular risk evaluation 1, 5
• ABI 1.00-1.40: Normal range 5, 2
• ABI >1.40: Noncompressible vessels—indicates medial arterial calcification; use toe-brachial index or alternative testing instead 5, 2

Common Pitfalls to Avoid

• Using only one ankle artery or the higher ABI between legs may miss significant unilateral disease—always use the lower ABI of both legs to identify patients at cardiovascular risk 5
• Failure to rest the patient adequately before measurement affects accuracy 5
• In patients with borderline values near 0.90, consider that the 95% confidence interval of measurement differences is 0.10; an ABI of 0.80 is sufficient to confirm PAD diagnosis in clinical practice 5

When Additional Testing Is Needed

• Anatomic imaging (duplex ultrasound, CTA, MRA, invasive angiography) is NOT required for initial PAD diagnosis 1
• Reserve imaging for symptomatic patients being considered for revascularization 1
• Duplex ultrasound serves as the first-line imaging method after ABI screening to confirm PAD lesions and guide revascularization strategy 1, 2
• For patients with normal or borderline resting ABI but exertional limb pain, perform exercise treadmill ABI testing 2
• For noncompressible arteries (ABI >1.40), measure toe-brachial index or use Doppler waveform analysis 2

Prognostic Value Beyond Diagnosis

• ABI <0.90 or >1.40 independently predicts increased cardiovascular events and mortality, regardless of PAD symptoms or other risk factors 5, 6
• ABI provides incremental prognostic information beyond standard cardiovascular risk scores 5
• There is an inverse, nonlinear correlation between ABI values and cardiovascular mortality, with very low ABI (<0.3) conferring significantly higher risk 6