What is the best test to assess claudication of the legs?

Best Test to Assess Claudication of the Legs

The ankle-brachial index (ABI) is the first-line diagnostic test to assess claudication, with a value <0.90 confirming peripheral arterial disease. 1

Initial Diagnostic Approach

Measure the ABI as the primary screening and diagnostic test after clinical examination in any patient with suspected claudication. 1 This test has 75% sensitivity and 86% specificity for diagnosing lower extremity arterial disease (LEAD). 1

Critical Technical Requirements:

• Measure blood pressure in both arms first and use the higher systolic pressure for calculations 1, 2
• Measure ankle pressures at both the dorsalis pedis and posterior tibial arteries 1
• Calculate ABI by dividing the higher ankle pressure by the higher arm pressure for each leg 1

When ABI Results Are Equivocal or Normal

If the resting ABI is normal (>0.90) or borderline (0.90-1.00) but clinical suspicion remains high:

Perform exercise treadmill testing with pre- and post-exercise ABI measurements. 1 This is the most objective test to:

• Confirm the diagnosis when resting ABI is normal 1
• Differentiate arterial claudication from pseudoclaudication (neurogenic causes) 1
• Quantify functional limitation by measuring pain-free and maximal walking distances 1

Diagnostic criteria for exercise testing:

• Post-exercise ankle systolic blood pressure decrease >30 mmHg, OR 1
• Post-exercise ABI decrease >20% confirms LEAD 1, 2

Use the Strandness protocol (3 km/h speed, 10% slope) for standardization and reproducibility. 1

When ABI Is Unreliable

If ABI is >1.40 (indicating noncompressible vessels from medial calcification, common in diabetes or chronic kidney disease):

Use the toe-brachial index (TBI) as the alternative first-line test. 1 A TBI <0.70 indicates peripheral arterial disease. 2 This is particularly important because ABI sensitivity is significantly reduced in diabetic patients. 1, 3

Alternative tests when vessels are noncompressible:

• Doppler waveform analysis of ankle arteries 1
• Pulse volume recordings 1

Common Pitfalls to Avoid

Do not rely solely on resting ABI in symptomatic patients with normal values - this misses a significant proportion of cases, particularly those with proximal stenoses that only manifest during exercise. 1, 2 The sensitivity of ABI drops to 61% in certain populations, particularly elderly patients, those with diabetes, and those with distal lesions. 3

Do not skip bilateral arm blood pressure measurement - failing to identify the higher arm pressure leads to inaccurate ABI calculations and potential misdiagnosis. 1, 2

Do not assume ABI correlates strongly with symptom severity - while ABI confirms the diagnosis, the correlation between ABI values and walking capacity or quality of life is weak (r = 0.278-0.343), so functional assessment requires additional testing. 4

Anatomic Imaging (Secondary Tests)

Once PAD is confirmed by ABI or exercise testing, duplex ultrasound (DUS) is the first-line imaging method to assess anatomy and hemodynamics. 1 DUS has 85-90% sensitivity and >95% specificity for detecting stenosis >50%. 1

Reserve CT angiography or MR angiography for when revascularization is being considered, as these provide the roadmap needed for intervention planning. 1