ANKLE-BRACHIAL INDEX (ABI)

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The ankle-brachial index (ABI) is a simple, rapid, non-radiological, non-invasive and highly valuable test  that can be easily performed in the clinic to analyse your risk of peripheral artery disease (PAD).

 

What is Peripheral Artery Disease (PAD)?

PAD is a serious condition where the arteries of the legs (lower extremities) are narrowed or blocked due to build-up of cholesterol in the arterial walls resulting in poor circulation, (i.e. restriction of flow of oxygen-rich blood).  People with PAD are at increased risk of heart attack and stroke and both cardiovascular and overall mortality.  This condition may occur in about 4% in the healthy adult population over the age of

40 years old to as high as 30% in patients in patients who

undergo screening in a primary care setting with diabetes,

cigarette smoking and age as risk factors.

 

How is ABI obtained?

ABI is derived from ratio of measuring and comparing the systolic blood pressure of the lower extremities (leg) at the ankle region to the systolic blood pressure at the upper arm (brachial region). The severity of peripheral arterial disease can therefore be determined by using this ratio also called the index number.  The lower the index, the more severe the condition.  Of special important is a ABI index of < 0.9 – this indicates lower blood pressure at the ankle compared to the arm and implies that there is narrowing or blockage of the arteries in the legs.  The full interpretation of ABI is outlined below :

Ankle Brachial Index Number
1.0 to 1.4 = normal (because the pressure between the lower extremities (leg)  and arm

should be almost the same or a little higher in the lower extremities).

0.99 to 0.91 = borderline; considered for additional cardiovascular risk testing
≤0.9 to 0.8 = mild PAD
≤0.8 to 0.5  = moderate PAD
<0.5 = severe PAD
>1.4 = rigid or hardened artery which are not compressible
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Note:

  • Although atherosclerosis (i.e. cholesterol deposition in arteries) affect all blood vessels, the     effect is greater in the leg than the arm arteries resulting in a lower ABI index.
  • PAD is under diagnosed and under-recognised in the community
  • Only 25% of patients with PAD are being treated appropriately.  This low percentage is largely  due to the unawareness in the general population.
  • In ABI decrease of 0.15 or more with time is useful to diagnose PAD progression.
  • A decrease in ABI by 20% or more after exercise is also very suspicious of PAD.
PERIPHERAL ARTERY DISEASE
ATHEROSCLEROSIS

NARROWED LEG ARTERY

FIBROUS PLAQUE FORMATION

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