What is an ankle-brachial index?: “The Ankle Brachial Index (ABI) is the systolic pressure at the ankle, divided by the systolic pressure at the arm. It has been shown to be a specific and sensitive metric for the diagnosis of Peripheral Arterial Disease (PAD). Additionally, the ABI has been shown to predict mortality and adverse cardiovascular events independent of traditional CV risk factors. The major cardiovascular societies advise measuring an ABI in every smoker over 50 years old, every diabetic over 50, and all patients over 70.” Stanford University Medical School
A normal ABI should be greater than or equal to 1. An ABI of 0.9 is 95% sensitive for finding some degree of occlusive disease on arteriography. And ABI of 0.41-0.9 represents disease that is usually associated with claudication. An ABI of 0.4 represents advanced disease.
Interpreting ABI measurements: Normal values defined as 1.00 to 1.40; abnormal values defined as 0.90 or less (i.e. ≤ 0.90); and borderline values defined as 0.91 to 0.99. Values greater than 1.40 indicate noncompressible vessels and are unreliable.
The lower the ABI, the more severe PAD. Incompressible vessels may be seen in elderly patients and people with long-standing diabetes.
** An ABI of >1.4 represents non-compressible arteries and may be a marker for artery calcification. In such situations, toe-brachial index (TBI) should be measured.
A toe-brachial index may be used in people with incompressible arteries of the more proximal lower extremity.
“Diagnosis of lower extremity PAD should also be confirmed with toe-brachial index measurement in persons with noncompressible vessels in whom ABI measurement is not reliable (e.g., those with long-standing diabetes mellitus, older persons), or with segmental pressure measurement when determining the anatomic location is necessary to make treatment decisions. ” AFP 2012
References
http://www.mayoclinic.org/tests-procedures/ankle-brachial-index/basics/definition/prc-20014625
http://stanfordmedicine25.stanford.edu/the25/ankle.html (Last Accessed 10/10/2017)
A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. 2011 ACCF/AHA Focused Update of the Guideline for the Management of Patients With Peripheral Artery Disease (Updating the 2005 Guideline). Journal of the American College of Cardiology. 2011;58(19):2020-2045. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4714326/
Am Fam Physician. 2012 May 15;85(10):1000-1001. ACCF/AHA Update Peripheral Artery Disease Management Guideline.