ABC of Vascular Disease
Ankle Brachial Pressure Index (ABPI)
1. What is an ABPI?
An ABPI is a quick, simple, non-invasive method of measuring the effect that
arterial disease is having on the blood pressure in the lower leg.
2. How is the ABPI measured?
If there is arterial disease in the arteries of the leg the blood pressure at
the foot is reduced (see Haemodynamics).
The degree of reduction of the blood pressure is a measure of the severity of
the arterial disease. The ABPI is measured in just the same way as the
blood pressure is measured in the arm: with a cuff that is wrapped around the
leg and inflated until the pressure in the cuff is the same as the pressure in
the artery just under the skin. The only difference is that a special
probe is used to listen to blood flow in the artery rather than a
stethoscope. Normally, the pressure in the leg is compared with the
equivalent pressure in the arm to see what proportion of pressure is lost by the
damaged arteries. This ratio of ankle blood pressure to brachial (arm)
blood pressure pressure is called the ankle brachial pressure index or
3. What is a normal and an abnormal ABPI?
An ABPI of greater than 0.9 (90%) is considered to be normal. An ABPI of
beween 0.5 and 0.9 (50% to 90%) is consistent with symptoms of Intermittent Claudication.
An ABPI of less than 0.5 (50%) is usually associated with more severe symptoms,
even Critical Ischaemia.
4. How reliable is the ABPI measurement?
In most patients it is a very reliable measure of the severity of arterial
disease. There are a number of situations where the ABPI is less reliable: