How to Order an Ankle-Brachial Index (ABI) for Left Lower Extremity
To properly order an ABI for the left lower extremity, request a "Doppler ankle-brachial index with measurement of both brachial pressures and left ankle pressures (posterior tibial and dorsalis pedis arteries)." 1, 2
Standard ABI Measurement Procedure
- The patient should be placed in a supine position and rested for at least 5 minutes before measurement 1, 2
- Blood pressure cuffs should be applied to both arms and the left ankle 1
- For the ankle cuff, placement should be 2 cm above the superior aspect of the medial malleolus 1
- An 8-10 MHz Doppler probe with gel should be used to detect arterial flow signals 1
Proper Measurement Sequence
- First arm systolic blood pressure (usually right arm) 1, 2
- Left posterior tibial (PT) artery pressure 1, 2
- Left dorsalis pedis (DP) artery pressure 1, 2
- Second arm systolic blood pressure 1, 2
- If the difference between first and second arm measurements exceeds 10 mmHg, disregard the first measurement and use only the second 1, 2
ABI Calculation
- ABI is calculated by dividing the highest ankle pressure (from either PT or DP artery) by the highest brachial pressure 1, 2
- Normal ABI range: 1.01-1.40 1, 2
- Borderline ABI: 0.91-1.00 1, 2
- Abnormal ABI (indicating PAD): <0.90 1, 2
- Non-compressible vessels: >1.40 (requires alternative testing) 1, 2
Additional Considerations
- For patients with suspected non-compressible vessels (common in diabetes or chronic kidney disease), request toe-brachial index (TBI) measurement as well 1
- For borderline results or when clinical suspicion remains high despite normal resting ABI, consider requesting an exercise ABI test 1
- Doppler waveform analysis should be included with the ABI measurement for more comprehensive assessment 1
Common Pitfalls to Avoid
- Using only one ankle artery measurement may miss significant disease; both PT and DP should be measured 2, 3
- Failure to rest the patient adequately before measurement can affect results 1, 2
- Not recognizing that ABI has moderate sensitivity (72.3%) and specificity (69.3%) when used alone; abnormal results may require confirmation with duplex ultrasound 4
- In diabetic patients, using the lower ankle pressure rather than the higher one may provide better diagnostic accuracy 3
By following these guidelines, you'll ensure proper measurement and interpretation of the ABI for assessment of peripheral arterial disease in the left lower extremity.