WOCN Position on Ankle-Brachial Index (ABI) Tests
The Wound, Ostomy, and Continence Nurses Society (WOCN) recommends the ankle-brachial index (ABI) as a first-line non-invasive screening and diagnostic tool for lower extremity arterial disease (LEAD). 1
Clinical Importance of ABI Testing
- ABI is indicated as the first diagnostic step after clinical examination for detecting peripheral arterial disease (PAD), with a value <0.90 having 75% sensitivity and 86% specificity for diagnosing LEAD 2
- ABI measurement should be performed in both legs in all new patients with suspected PAD to establish a baseline and confirm diagnosis 2
- The WOCN Society recognizes ABI as an essential component in the screening and assessment of patients with wounds due to LEAD 1
- ABI is a powerful independent marker of cardiovascular risk, with values below 0.9 correlating with increased risk of non-fatal cardiac events and mortality 3
Proper ABI Measurement Technique
- ABI is calculated as the systolic blood pressure obtained at the ankle divided by the systolic blood pressure obtained at the brachial artery while the patient is lying down 2
- The higher of the brachial pressures should be used as the denominator for both right and left ratios, and the higher of the 2 ankle pressures (posterior tibial or dorsalis pedis) should be used as the numerator for each leg 2
- All four ankle arteries (bilateral dorsalis pedis and posterior tibial) should be assessed, as discordant values between arteries may indicate increased cardiovascular risk even when the highest value appears normal 4
Interpretation of ABI Values
- Normal ABI values range from 0.90 to 1.40 2
- An ABI <0.90 confirms PAD diagnosis 2
- Patients with borderline ABI (0.90–1.00) need further diagnostic tests 2
- When clinically suspected but ABI is normal (>0.90), post-exercise ABI and/or duplex ultrasound are necessary 2
- A post-exercise ABI decrease >20% is diagnostic for PAD 2
Special Considerations
- ABI sensitivity is poorer in patients with diabetes or end-stage chronic kidney disease due to medial calcification 2
- In case of high ABI (>1.40) related to medial calcification, alternative tests should be used 2:
- Toe pressure measurements
- Toe-brachial index (TBI)
- Doppler waveform analysis of ankle arteries
- Pulse volume recording
- The presence of triphasic pedal Doppler arterial waveforms largely excludes PAD, indicating healthy, elastic arterial walls with normal compliance 5
Clinical Applications
- ABI should be used to establish PAD diagnosis in patients with:
- Exertional leg symptoms
- Non-healing wounds
- Age ≥70 years
- Age ≥50 years with history of smoking or diabetes 2
- ABI is valuable for stratifying cardiovascular risk, with an inverse correlation between ABI values and cardiovascular events 3
- Regular ABI monitoring can be used for patient follow-up after revascularization procedures 2
- The WOCN Society emphasizes ABI as part of a comprehensive assessment for patients with wounds related to arterial insufficiency 1
Common Pitfalls and Limitations
- ABI has lower sensitivity (15-79%) in elderly individuals and patients with diabetes 6
- Despite high specificity (83.3-99.0%), ABI may miss some cases of significant stenosis 6
- Most primary care physicians do not routinely perform ABI in their office due to reimbursement issues and inadequate knowledge 7
- When using ABI for cardiovascular risk assessment, both abnormally low (<0.9) and abnormally high (>1.4) values correlate with increased risk of major adverse cardiovascular events 3
The WOCN Society's position aligns with other major cardiovascular societies in recognizing ABI as an essential tool for screening, diagnosis, and risk stratification in patients with suspected or confirmed LEAD.