What is an ankle-brachial index?
An ankle-brachial pressure index (ABPI) or ankle-brachial index (ABI) is the ratio of the systolic (upper) blood pressures (BP) of the ankle to the upper arm (brachium). Ankle BP is indicative of arterial disease. Lower ankle BP in the leg suggests blocked blood vessels due to peripheral artery disease (PAD) or atherosclerosis.
It is a simple procedure and cost-effective assessment that can be in an outpatient set up by a doctor, nurse, or trained medical professional. It helps to detect lower-extremity arterial narrowing in cases of diseases of peripheral blood vessels or in cases of a lower-extremity arterial injury after penetrating or blunt trauma.
An ABI less than 0.90 has been shown to have a sensitivity of 90% and a specificity of 98% for detecting lower-extremity stenosis of higher than 50%. During a trauma, an ABI less than 0.90 has been shown to have a sensitivity exceeding 87% and a specificity exceeding 97% for identifying a lower-extremity arterial injury.
How is an ankle-brachial index estimated?
The required equipment for measuring the ankle-brachial index (ABI) include the following:
- An appropriate-sized blood pressure (BP) cuff for the upper and lower extremities with a working sphygmomanometer (commonly referred to as a BP apparatus)
- A Doppler device for detecting flow
- Ultrasound transmission gel
- An examination table
No anesthesia is used during the procedure. Any form of a sedative or anesthesia may affect the BP measurement and thus reduce the accuracy of the ABI.
The procedure is performed with the patient lying down on an examination table.
What does a high ankle-brachial index mean?
Based on the results, the physician advises a treatment plan.
In a normal patient, the pressure at the ankle is slightly higher than at the elbow.
The ankle-brachial pressure index (ABPI) is the ratio of the highest ankle to brachial artery pressure. An ABPI ranging from 0.90-1.29 is considered normal (free from major peripheral artery disease [PAD]), whereas a lesser than 0.9 indicates an arterial disease.
An ABPI value of 1.3 or higher is also considered abnormal and suggests
- hardening, and
- narrowing of the vessel walls.
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