From the Guidelines
The Ankle-Brachial Index (ABI) test should be performed by measuring systolic blood pressures in both arms and ankles, then calculating the ratio of ankle to arm pressure, with the most recent guidelines from 2024 1 recommending the use of the higher systolic pressure in the ipsilateral dorsalis pedis and posterior tibial arteries divided by the higher of the left and right brachial artery systolic pressures. To conduct an ABI test, first have the patient rest supine for 5-10 minutes to stabilize blood pressure, as recommended by the American Heart Association in 2012 1. Using a blood pressure cuff and Doppler ultrasound probe with conducting gel, measure the systolic pressure in both brachial arteries and record the higher value. Then measure the systolic pressures in the posterior tibial and dorsalis pedis arteries of both ankles. For each leg, use the higher of these two ankle pressures to calculate the ABI by dividing the ankle pressure by the higher brachial pressure. A normal ABI ranges from 1.0-1.4, while values below 0.9 indicate peripheral artery disease (PAD), with severity increasing as the value decreases, as stated in the 2017 guidelines 1. Values above 1.4 suggest non-compressible arteries due to calcification, often seen in diabetes or kidney disease. The ABI is valuable because it provides an objective, non-invasive assessment of arterial blood flow to the lower extremities, helping diagnose PAD even before symptoms appear, as noted in the 2018 comparison of ACC/AHA and ESC guidelines 1. Some key points to consider when performing an ABI test include:
- The patient should be at rest for 5-10 minutes before the test, in a supine position, relaxed, with head and heels supported, and in a room with a comfortable temperature, as specified in the 2012 American Heart Association statement 1.
- The cuff should be chosen adequately according to the limb size, with a width that contours at least 40% of the limb circumference, and should not be applied over a distal bypass or over ulcers, as recommended in the 2012 guidelines 1.
- The ABI test typically takes 10-15 minutes to complete and requires minimal equipment, making it an efficient screening tool for vascular disease, as mentioned in the example answer.
- In cases where the ABI is >1.40, alternative methods such as the toe-brachial index, Doppler waveform analysis, or pulse volume recording may be indicated, as suggested in the 2018 guidelines comparison 1.
- The 2024 guidelines 1 emphasize the importance of using the ABI as a first-line noninvasive test for the diagnosis of PAD, and provide recommendations for the use and interpretation of the ABI in different clinical scenarios. Overall, the ABI test is a valuable tool for diagnosing and managing PAD, and should be performed and interpreted in accordance with the most recent guidelines and evidence-based recommendations.
From the Research
Procedure for Performing an Ankle-Brachial Index (ABI) Test
To perform an ABI test, the following steps can be taken:
- Measure the systolic blood pressure in both arms and both ankles using a Doppler ultrasonography device 2.
- Calculate the ABI by dividing the higher of the two systolic ankle pressures by the higher of the two systolic arm pressures (HABI method) or by dividing the lower of the two systolic ankle pressures by the higher of the two systolic arm pressures (LABI method) 3, 4.
- Compare the results to determine if there is a significant difference between the two methods, with the LABI method potentially being more sensitive in detecting peripheral arterial disease (PAD) 3, 4.
- Consider the position of the patient and the arm during measurement, as this can affect blood pressure readings 5.
Important Considerations
- The position of the body and arm can significantly influence blood pressure measurement, with supine positions potentially resulting in higher readings than sitting positions 5.
- The use of a Doppler ultrasonography device can help to accurately measure systolic blood pressure in the ankles and arms 2.
- The LABI method may be more accurate in detecting PAD, particularly in patients with diabetes or below-knee PAD 4.