Is Ankle-Brachial Index (ABI) alone sufficient for assessing lower extremity wounds?

ABI Alone is Not Sufficient for Lower Extremity Wound Assessment

ABI alone is inadequate for comprehensive assessment of lower extremity wounds and should be supplemented with additional vascular testing modalities to ensure accurate diagnosis and guide appropriate treatment decisions. 1

Limitations of ABI in Wound Assessment

• ABI may be normal (0.90 to 1.40) in nearly one-quarter of patients with chronic limb-threatening ischemia (CLTI), and 29% of patients with CLTI have an ABI between 0.70 and 1.40, making ABI alone unreliable for wound assessment 1
• The concordance between ABI and toe pressure/toe-brachial index (TBI) among patients with CLTI is poor, with only 58% of patients who meet criteria for abnormal toe pressures presenting with abnormal ABIs 1
• ABI has moderate diagnostic sensitivity (72.3%) and specificity (69.3%) when compared to duplex ultrasound as a reference standard 2
• False-negative results occur in approximately 27.5% of limbs with normal ABI values, meaning significant arterial disease may be missed if relying on ABI alone 2

Recommended Comprehensive Vascular Assessment for Lower Extremity Wounds

1. Initial Assessment

• Perform ABI measurement as a first-line test for patients with lower extremity wounds 1
• Document wound characteristics including location, size, depth, drainage, and tissue type 3
• Palpate pedal pulses as part of the comprehensive vascular examination 1

2. Additional Testing for Accurate Perfusion Assessment

• Toe pressure/TBI measurements should be performed, especially when ABI is normal or elevated (>1.40) due to noncompressible vessels 1
• Abnormal toe pressures (<30 mm Hg) reflect severe ischemia and are associated with decreased likelihood of wound healing 1
• Continuous-wave Doppler or photoplethysmographic waveforms from the base of the great toe provide additional diagnostic information 1
• Transcutaneous oxygen measurement (TcPO2) and skin perfusion pressure (SPP) should be considered for perfusion assessment 1, 4
• A TcPO2 >30 mm Hg or an SPP >40 mm Hg can predict wound healing potential 1

3. Anatomic Assessment When Revascularization is Considered

• For nonhealing wounds where revascularization may be necessary, anatomic imaging is required 1
• Duplex ultrasound, computed tomography angiography (CTA), magnetic resonance angiography (MRA), or catheter angiography should be performed to determine revascularization strategy 1

Clinical Decision Algorithm

1. For all lower extremity wounds:

   • Perform ABI measurement 1
   • If ABI ≤0.90: PAD is confirmed, but additional testing is needed to assess wound healing potential 1
   • If ABI 0.91-1.40: PAD cannot be ruled out; proceed with additional testing 1
   • If ABI >1.40: Vessels are noncompressible; TBI is mandatory 1

2. Additional perfusion assessment:

   • Measure toe pressures/TBI (abnormal if TBI ≤0.70) 1
   • Consider TcPO2 (target >30 mm Hg) or SPP (target >40 mm Hg) 1
   • Evaluate Doppler waveforms at the foot 1

3. For wounds with inadequate perfusion:

   • Obtain anatomic imaging (duplex ultrasound, CTA, MRA, or catheter angiography) if revascularization is being considered 1
   • Consider revascularization for toe pressure <30 mm Hg, TcPO2 <30 mm Hg, or SPP <40 mm Hg 1, 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
• Perfusion assessment measures (TBI, TcPO2, SPP) should be obtained in a warm room to prevent arterial vasoconstriction in response to cold, which could lead to inaccurate results 1
• For patients with nonhealing wounds with normal perfusion assessment, alternative diagnoses should be considered 1
• Normal range ABI outcomes cannot be taken to infer the absence of PAD; further arterial imaging should be strongly considered in those with suspected underlying disease 2