The ABPI is such a helpful and widely used test that it is worth devoting a whole chapter to it. It is:

• highly sensitive and specific for the presence of peripheral vascular disease
  
• non-invasive
  
• quick, cheap and easy to perform
  
• reproducible.

The premise of the ABPI lies in measuring a pressure difference between the arm, reflecting systemic pressure, and the foot. Because the arm is rarely affected by arterial occlusive disease, the arm pressure is used as the ‘norm’ (i.e. the denominator) and the foot pressure is the numerator. To be precise, it is the systolic pressure in one of the two foot pulses (whichever one is highest) divided by the brachial artery systolic pressure.