Tests for Blood Circulation in Legs
The ankle-brachial index (ABI) is the cornerstone first-line non-invasive test for evaluating blood circulation in the legs, followed by duplex ultrasound when more detailed anatomical information is needed. 1
Primary Diagnostic Tests
Ankle-Brachial Index (ABI)
- ABI is measured using a blood pressure cuff and a Doppler device to detect blood flow in pedal and brachial arteries 1
- Normal ABI ranges between 0.9-1.3; values <0.9 suggest peripheral artery disease (PAD) 1
- ABI has 75% sensitivity and 86% specificity for diagnosing lower extremity arterial disease 1
- Can be performed in vascular laboratory or office-based setting 1
- Limitations: reduced sensitivity in patients with diabetes or chronic kidney disease due to noncompressible vessels 1
Toe-Brachial Index (TBI)
- Recommended when ABI >1.40 due to noncompressible vessels 1
- Normal TBI is >0.70; abnormal is <0.70 1
- More accurate for PAD assessment in patients with diabetes and chronic kidney disease 1
Exercise Treadmill Test with ABI
- Useful for patients with normal resting ABI but symptoms suggestive of PAD 1
- A post-exercise ABI drop >20% or ankle pressure decrease >30 mmHg is diagnostic for PAD 1
- Helps differentiate vascular claudication from neurogenic claudication 1
Advanced Physiological Testing
Pulse Volume Recording (PVR)
- Provides qualitative measurement of limb perfusion 1
- Creates waveform tracings showing volume changes with each pulse 1
- Useful in patients with noncompressible vessels 1
- Can confirm presence and severity of PAD 1
Segmental Pressure Measurements (SPM)
- Compares systolic pressures at sequential levels in extremities 1
- A pressure drop of 20 mmHg between adjacent measurements suggests significant stenosis 1
- Helps distinguish approximate level of disease 1
Transcutaneous Oxygen Pressure (TcPO2)
- Determines oxygen tension within tissue 1
- Values >40 mmHg around ulcer or amputation sites predict successful healing 1
- Useful in patients without pedal Doppler signals 1
Imaging Tests
Duplex Ultrasound (DUS)
- Combines grayscale 2D imaging, color Doppler, and spectral waveform analysis 1
- Provides extensive information on arterial anatomy and blood flow 1
- 85-90% sensitivity and >95% specificity for detecting >50% diameter stenosis 1
- Widely available, portable, and doesn't require contrast agents 1
- Operator-dependent; requires adequate qualification and training 1
Computed Tomography Angiography (CTA)
- 96-98% sensitivity and 94-98% specificity for detecting aorto-iliac stenoses >50% 1
- Advantages: visualization of calcifications, clips, stents, bypasses, and aneurysms 1
- Limitations: radiation exposure, contrast nephrotoxicity, allergies 1
Magnetic Resonance Angiography (MRA)
- 95% sensitivity and specificity for diagnosing segmental stenosis and occlusion 1
- Tends to overestimate degree of stenosis 1
- No radiation exposure 1
Diagnostic Algorithm
Initial Assessment: Perform resting ABI with or without PVR/Doppler waveforms 1
- If ABI <0.9: PAD diagnosis confirmed
- If ABI >0.9 but symptoms present: Proceed to exercise treadmill ABI
- If ABI >1.40 (noncompressible vessels): Use TBI, TcPO2, or SPP
Secondary Assessment: If PAD confirmed and symptoms are functionally limiting despite conservative management 1
- Perform segmental pressures with PVR and/or Doppler waveforms
- If revascularization is being considered, proceed to anatomical imaging
Anatomical Assessment: If revascularization is being considered 1
- Duplex ultrasound, CTA, MRA, or catheter angiography to assess anatomy
Common Pitfalls and Caveats
- ABI has limited usefulness in localizing disease or distinguishing between single-level and multilevel disease 1
- Noncompressible vessels (ABI >1.40) commonly occur in patients with diabetes and chronic kidney disease 1
- Vessel calcification can lead to falsely elevated pressure readings 1
- Using small cuffs on large limbs can result in spuriously high pressure readings 2
- Doppler ultrasound reliability varies based on operator experience and environmental factors 3