The ankle-brachial pressure index is calculated by:
ABPI = (ankle systolic BP)/(brachial systolic BP)
Interpretation of results is not entirely straightforward as various consensus papers give different cut -offs for the definitions of 'moderate' and 'severe'. One set of definitions is:
- >1.4: calcification may be present
- >1.0 probably no arterial disease
- 0.81-1.0 no significant arterial disease
- 0.5-0.8 moderate disease
- <0.5 severe disease
- <0.3 critical ischaemia
It is worth noting that an ABPI <0.9 or of >1.4 is an independent risk factor for cardiovascular disease.
ABPI may be non-diagnostic in patients with heavy arterial calcification, such as:
- diabetics (5-10% of diabetic patients cannot have their occlusive ankle pressure measured)
- the elderly
- renal failure
