What is the proper procedure for writing an order for an ankle brachial index (ABI) test?

How to Write an Order for Ankle-Brachial Index Test

To properly order an ankle-brachial index (ABI) test, specify "Ankle-Brachial Index Test" with instructions to measure systolic pressures in both arms and both ankles (posterior tibial and dorsalis pedis arteries) to calculate the ratio of ankle to brachial systolic pressure. 1

Essential Components of the ABI Order

• Specify "Ankle-Brachial Index Test" as the procedure name 1
• Include clinical indication for the test (e.g., suspected peripheral arterial disease, leg pain with exertion, non-healing wounds) 1
• Request bilateral measurements (both legs) to establish baseline and confirm diagnosis 1
• Specify that both posterior tibial (PT) and dorsalis pedis (DP) arteries should be measured at each ankle 1
• Request measurement of both brachial arteries 1

Recommended Measurement Sequence

• Order the measurement sequence as: first arm, first PT artery, first DP artery, other PT artery, other DP artery, and other arm 1
• If the systolic blood pressure of the first arm exceeds the second arm by >10 mm Hg, specify that the first arm should be remeasured 1

Special Considerations for the Order

• For diagnostic purposes, specify that the higher ankle pressure should be used to calculate the ABI (improves specificity) 1, 2
• For patients with suspected non-compressible vessels (e.g., patients with diabetes or advanced age), include an order for toe-brachial index as an alternative 1, 2
• For patients with normal resting ABI but suspected PAD, consider adding a post-exercise ABI measurement 2, 3

Interpretation Guidelines to Include

• Normal ABI: 0.91-1.40 2
• Borderline: 0.91-0.99 2
• Abnormal (indicating PAD): ≤0.90 2
• Non-compressible arteries: >1.40 2

Common Pitfalls to Avoid

• Failing to order bilateral measurements, which could miss unilateral disease 1
• Not specifying measurement of both PT and DP arteries, which could miss disease affecting only one vessel 1
• Overlooking the need for toe-brachial index in patients likely to have calcified vessels 1, 2
• Not considering exercise ABI when resting values are normal but clinical suspicion remains high 2, 3

Sample Order Format

Order: Ankle-Brachial Index Test
Clinical Indication: [Specify indication - e.g., suspected PAD, leg pain with exertion]
Instructions:
- Measure systolic pressures in both brachial arteries
- Measure systolic pressures in both posterior tibial and dorsalis pedis arteries
- Calculate ABI using higher ankle pressure for diagnostic purposes
- Follow recommended measurement sequence: first arm, first PT, first DP, other PT, other DP, other arm
- If first arm pressure exceeds second arm by >10 mm Hg, repeat first arm measurement
- If ABI >1.40 or arteries non-compressible, perform toe-brachial index

Remember that ABI has moderate diagnostic accuracy with sensitivity ranging from 68% to 84% and specificity from 84% to 99% 3, 4. When clinical suspicion remains despite normal ABI results, additional testing such as duplex ultrasound may be warranted 4.