An ankle-brachial index is a simple and non-invasive test performed to diagnose peripheral vascular disease. The index compares the blood pressure of the legs and arms and creates a ratio that shows the availability of blood to flow freely from one extremity to the other. The ABI is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressure in the arm.
During this test, patients lie on their back and a technician places blood pressure cuffs on the ankles and arms. The machine then inflates the cuffs alternating to get the ratio. This test may include exercise by walking on a treadmill for several minutes in order to simulate when a patient would feel pain due to peripheral artery disease and then takes the reading afterward to understand the severity of the said disease.
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https://vascular.org/patient-resources/vascular-tests