Is Ankle-Brachial Index (ABI) recommended for all lower extremity wounds?

ABI Testing for Lower Extremity Wounds

ABI testing should be performed for all patients with lower extremity wounds as part of a comprehensive vascular assessment, but it should not be used as the sole diagnostic tool due to its limitations in certain patient populations. 1

Indications for ABI Testing in Lower Extremity Wounds

• ABI testing is recommended as a first-line test for all patients with lower extremity wounds to establish diagnosis of peripheral artery disease (PAD) 2, 3
• The resting ABI should be used to establish lower extremity PAD diagnosis in patients with suspected PAD, including those with nonhealing wounds, age ≥65 years, or age ≥50 years with history of smoking or diabetes 2
• ABI should be measured in both legs in all new patients with PAD of any severity to confirm diagnosis and establish a baseline 2
• ABI results should be uniformly reported with noncompressible values defined as >1.40, normal values 1.00-1.40, borderline 0.91-0.99, and abnormal ≤0.90 2

Limitations of ABI in Wound Assessment

• ABI may be normal in nearly one-quarter of patients with chronic limb-threatening ischemia, making it unreliable as the sole assessment tool 1, 3
• The concordance between ABI and toe pressure/toe-brachial index among patients with chronic limb-threatening ischemia is poor, with only 58% of patients who meet criteria for abnormal toe pressures presenting with abnormal ABIs 1, 3
• ABI has moderate predictive value in diagnosing lower extremity arterial disease, with sensitivity of 72.3% and specificity of 69.3% when using duplex ultrasound as a benchmark 4
• ABI may be falsely elevated in patients with diabetes and renal failure due to calcification of arteries, causing them to be noncompressible 5, 6

Comprehensive Vascular Assessment Approach

• For all lower extremity wounds, perform ABI measurement as initial assessment 1, 3
• If ABI ≤0.90, PAD is confirmed, but additional testing is needed to assess wound healing potential 1, 3
• If ABI >1.40, vessels are noncompressible, and toe-brachial index (TBI) is mandatory 1, 3
• Toe pressure/TBI measurements should be performed, especially when ABI is normal or elevated due to noncompressible vessels 1
• The toe-brachial index should be used to establish lower extremity PAD diagnosis in patients with suspected PAD but in whom ABI test is not reliable due to noncompressible vessels (usually patients with long-standing diabetes or advanced age) 2

Additional Vascular Assessment Tools

• Leg segmental pressure measurements are useful to establish lower extremity PAD diagnosis when anatomic localization is required to create a therapeutic plan 2
• Perfusion assessment measures such as transcutaneous oxygen pressure (TcPO2) and skin perfusion pressure (SPP) can predict wound healing potential, with TcPO2 >30 mm Hg or SPP >40 mm Hg 1, 3
• When diagnostic uncertainty exists, consider additional noninvasive tests such as pulse volume waveforms 4

Common Pitfalls and Caveats

• Relying solely on ABI may miss significant arterial disease in patients with diabetes or advanced age due to arterial calcification causing falsely elevated readings 1, 3
• Normal range ABI outcomes cannot be taken to infer the absence of PAD; further arterial imaging should be considered in those with suspected underlying disease requiring intervention 4
• Perfusion assessment measures should be obtained in a warm room to prevent arterial vasoconstriction in response to cold, which could lead to inaccurate results 1
• False-negative ABI results can occur in 27.5% of limbs, potentially missing significant vascular pathology 4