Arterial Physiologic ABI TBI

Lower Extremity Pressures

1. Ankle/Brachial Index (ABI) Calculation

a. Divide ankle pressures by highest of the two brachial pressures

b. The higher of the two ipsilateral pressures is used to report the ABI for a limb

c. Interval change of 0.15 between visits/exams is considered significant

ABI Disease categories

• Medial calcification of the arterial wall may create falsely elevated (unreliable) pressures which is reported when the resting ABI exceeds 1.30.  Note that the ABI may also be reported as falsely elevated if it is normal and waveforms are clearly abnormal.

     • Absolute ankle pressure <40 mmHg indicates ischemic ulcers are unlikely to heal.

2.   Toe/Brachial Index (TBI) Calculation - Divide toe pressure by the highest of the two brachial pressures

TBI Disease categories

     • Absolute toe pressure <30 mmHg is associated with critical ischemia.

     • Absolute toe pressure >55 mmHg has been correlated with the ability to heal a foot ulcer in diabetic patients.