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5 Things You Need to Know About: ABIs

Goldman, Robert J. MD

Section Editor(s): Hess, Cathy Thomas BSN, RN, CWOCN

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5 Things You Should Know About ABIs

The ankle-brachial index (ABI) is a simple, noninvasive test that assesses for the presence of arterial insufficiency. Systolic blood pressure is measured over the brachial artery and the posterior tibial artery. The ankle pressure, measured using a handheld Doppler, should be the same as or slightly higher than the brachial pressure. As the valve diminishes, a declining ABI correlates with worsening of arterial insufficiency. An exceedingly low ABI contraindicates the use of compression therapy until further evaluation for the presence of arterial disease is performed.

The clinician should keep in mind these 5 essential tips when performing or interpreting an ABI:

  1. Combined with other tests, such as pulse-volume recordings, the ABI can indicate the presence of large-vessel arterial disease—stenosis or blockage of the arteries of the pelvis, thigh, leg, and/or ankle.
  2. Because 2 larger arteries cross the ankle, the ABI really has 2 parts: the posterior tibial (medial ankle) and the anterior tibial (usually measured at the dorsalis pedis on the foot dorsum).
  3. The ABI may be falsely elevated in patients with diabetes mellitus or end-stage renal disease due to calcified vessels. These patients should undergo further testing to determine arterial sufficiency.
  4. The numerical limits given in Interpreting the ABI should be used only as a guideline. Patients can have a very low ABI (<0.5) but tolerate compression and heal well. The reason? Good collateralization can exist around large-vessel arterial blockages, leading to good skin oxygenation. Oxygenation is measurable by TcPo2 on the foot. A normal TcPo2 (TcPo2 >50 over several anatomic regions or segments) and ABI (ABI <0.5) may indicate that judicious use of standard compression will be effective.
  5. Critical ischemia determined by the ABI (ABI <0.5) requires clinical correlation. Look for the typical purple hue of ischemic skin, rapidly expanding cutaneous gangrene, and/or pain at rest.

Interpreting the ABI

Use the following guideline to interpret the ABI results:

  • 0.9 to 1—normal
  • 0.75 to 0.9—moderate arterial disease
  • 0.5 to 0.75—severe arterial disease
  • below 0.5—limb-threatening
© 2003 Lippincott Williams & Wilkins, Inc.