The ankle-brachial index (ABI) is considered the primary diagnostic test for PAD. An ABI < 0.9 is up to 95% sensitive and 99% specific for the detection of angiographically confirmed PAD . A simple ABI test can be performed in the office setting, using a hand-held Doppler device (5- or 10-MHz) with acoustic gel and appropriately sized (10-12 cm) blood pressure cuffs. With the patient resting in a supine position, the ABI is obtained by measuring the systolic pressure at the bilateral brachial, anterior tibial, and posterior tibial arteries. The ABI for each leg is calculated by dividing the higher of the two ankle systolic pressures by the higher of the two brachial pressures . The ABI measurement technique is illustrated in FIGURE 1.
An ABI < 0.9 establishes the PAD diagnosis. The ABI is also considered an adequate measure of overall lower extremity perfusion and therefore can be readily used to quantify disease severity as shown in the table:
Limitations of the ABI:
- Medial arterial calcification resulting in non-compressible arteries may lead to false elevation (ABI > 1.4) or artificial normalization of ABI
- ABI may be normal or borderline at rest in patients with aortoiliac disease