Ankle-Brachial Index (ABI) Measurement Technique

Updated: Sep 10, 2020
  • Author: Chan W Park, MD, FAAEM; Chief Editor: Karlheinz Peter, MD, PhD  more...
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Technique

Approach Considerations

Different values obtained for the ankle-brachial index (ABI) are interpreted as follows: [15, 16]

  • 0.00 to 0.40 - Severe peripheral arterial disease (PAD) sufficient to cause resting pain or gangrene
  • 0.41 to 0.90 - PAD sufficient to cause claudication
  • 0.91 to 1.30 - Normal vessels
  • >1.30 - Noncompressible, severely calcified vessel

Patients with an ABI lower than 0.90 have a higher risk of coronary artery diseasestroke, and death and therefore should be referred to a credentialed vascular laboratory for further testing. Such testing may include computed tomography (CT), magnetic resonance imaging (MRI), or conventional angiography, all of which involve injecting contrast material in order to assess the arterial flow. [7]

For accuracy, systolic blood pressure readings should be obtained from both arms, and the higher of the two values—not the average of the two—should be used in the ABI calculation. Two systolic blood pressure readings should be obtained from each ankle, and again, the higher of the two values should be used. 

Claudication is a specific but not a sensitive finding in patients with PAD. One study stated that up to 90% of patients with a documented ABI lower than 0.90 did not report claudication as a symptom. [3, 7, 16]

An ABI of 0.91-0.99 is considered borderline. The patient may be asymptomatic at rest but may experience symptoms related to the compromised vascular flow when ambulating. An exercise test may help evaluate a patient who has borderline ABI results.

An incorrectly performed test may lead to a false-negative or a false-positive result and thereby delay the diagnosis or prompt unnecessary further testing. A false-negative ABI result may occur in patients with noncompressible arteries—that is, a heavily calcified lower-extremity vessel may artificially elevate ankle pressure measurement.

Next:

Measurement of Ankle-Brachial Index

Place the patient in the supine position, with the arms and legs at the same level as the heart, for a minimum of 10 minutes before measurement

Select an appropriately sized blood pressure cuff for both the ankle and the arms (see the images below); the cuff width should be, at a minimum, 40% of the extremity circumference. The ankle cuff should go on the leg between the malleolus and the calf. Enough room should be left below both cuffs to permit placement of the ultrasound gel, so that the Doppler device can adequately detect the brachial, dorsalis pedis, and posterior tibial pulses. [7, 16]

Pick appropriately sized cuff on basis of width of Pick appropriately sized cuff on basis of width of lower extremity.
Make sure that cuff completely encircles lower ext Make sure that cuff completely encircles lower extremity.
Make sure you have appropriately sized upper-extre Make sure you have appropriately sized upper-extremity cuff. Note that patient is in supine position.

Obtain the brachial systolic pressures of both arms (see the images below), and choose the higher of the two values as the brachial systolic pressure (the difference between them should be less than 10 mm Hg). The brachial pulse is best appreciated on the medial side of the antecubital fossa.

Do not obscure artery with cuff; you will need to Do not obscure artery with cuff; you will need to be able to palpate artery and/or locate it with Doppler device.
As with each appropriately identified arterial sit As with each appropriately identified arterial site, mark site with ultrasound transmission gel after palpation.
Locate artery with device. Typically, Doppler prob Locate artery with device. Typically, Doppler probe must be positioned at 45-60 degrees, not at 90 degrees as shown.

Obtain the anterior tibial and posterior tibial systolic pressures of the extremity in question (see the images below), and select the higher of the two values as the ankle pressure measurement. The posterior tibial pulse is best appreciated just dorsal and inferior to the medial malleolus. The dorsalis pedis pulse is best appreciated on the dorsum of the foot between the proximal section of the first and second metatarsals, usually above the navicular bone.

Palpate artery. Dorsalis pedis is palpated by hand Palpate artery. Dorsalis pedis is palpated by hand before Doppler device is used.
Place small amount of ultrasound transmission gel Place small amount of ultrasound transmission gel at landmark where artery was located.
Locate artery with Doppler device. Locate artery with Doppler device.
Posterior tibial artery is located and marked with Posterior tibial artery is located and marked with gel.
Identify artery with Doppler device. Upon applicat Identify artery with Doppler device. Upon application of Doppler probe, arterial pulsations should be audible. If they are not, reposition probe until appropriate sound is obtained.

Finally, divide the ankle systolic pressure by the brachial artery systolic pressure; the result is the ABI.

Alternative techniques for measuring the ABI have been reported. Ichihashi et al assessed the diagnostic ability and reproducibility of a four-cuff automated oscillometric device as an alternative to the Doppler method for obtaining ABI measurements. [8]  With Doppler ABI measurement as the reference, oscillometric ABI measurement was found to have a sensitivity of 89.1%, a specificity of 94.4%, an accuracy of 94.1%, a positive predictive value of 91.8%, and a negative predictive value of 92.4%. Hageman et al also found oscillometric ABI measurement to have good diagnostic accuracy for PAD but noted the substantial incidence of oscillometric errors. [14]

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