Ankle-Brachial Index (ABI) Test
The ankle-brachial index (ABI) test is a quick and non-invasive assessment of the peripheral
blood vessels to test for peripheral vascular disease. The ABI is the ratio of blood pressure in the
brachial artery of the arm and in the lower legs. A large difference in the two pressures, signals
peripheral artery disease (PAD).
PAD does not always cause symptoms. Many patients who have PAD don’t know it. They may
even experience symptoms, such as pain, cramping or tingling in the legs, but often do not
report it, believing it is a natural part of aging or caused by something else.
PAD develops when arteries become clogged with plaque (atherosclerosis) and limits the
blood flow to the legs. Clogged arteries in the legs are a major risk factor for having a heart
attack or stroke.
The American Heart Association reports that people with PAD have a four to five times greater
risk of having a heart attack or stroke.
PVD results from atherosclerosis and inflammation and can then lead to stenosis, an embolism
Peripheral vascular disease is more common in smokers and people with diabetes.
Toe-Brachial Index (TBI) Assessment
The ankle – brachial pressure index (ABI) is a simple, useful method for diagnosing Peripheral
Arterial Disease (PAD). In determining the severity of PAD in a lower extremity, the toe-brachial
index (TBI) is used.
Due to both lifestyle and genetic reasons, arteries may become hardened. This atherosclerotic
condition may not cause painful symptoms until the artery is narrowed 60% or more. A blood
clot or piece of cholesterol or calcium that may break off and move into the artery could cause
a blockage that would disrupt blood flow. The legs are the area of the body most commonly
damaged by PAD.
Severe PAD may lead to Critical Limb Ischemia, where blockages have become so severe that
legs and feet are no longer receiving blood flow.
The degree of PAD depends on when it is diagnosed and other present risk factors such as
smoking, high cholesterol, heart disease and diabetes.
The Toe-Brachial Index (TBI) Process
The test is performed using a photoplethysmograph (PPG) infrared light sensor on the left
finger and the right toe, while the patient is in a reclining position. The resultant Toe-Brachial
Index (TBI) is generated using readings from the finger and toe. A TBI reading is done for each
leg. 0.75 TBI is considered normal.