When the ankle-brachial index test is complete, your doctor calculates your ankle-brachial index by dividing the higher of the two blood pressure measurements at the arteries near your ankle by the higher of the two blood pressure measurements at your arms. Based on the number your doctor calculates, your ankle-brachial index may show you have:
- No blockage (1.0 to 1.4). An ankle-brachial index number in this range suggests that you probably don't have peripheral artery disease. But if you have certain risk factors, such as diabetes, smoking or a family history of PAD, tell your doctor so that he or she can continue to monitor your risk.
- Borderline (0.9 to 0.99). If your ankle-brachial index number is less than 1.0, you may have some narrowing of the arteries in your leg. People with an ankle-brachial index of 0.9 or lower may have the beginnings of PAD. Your doctor may then monitor your condition more closely.
- Mild blockage (0.8 to 0.89). An ankle-brachial index in this range shows you're in the early stages of PAD. Your doctor may suggest medications or lifestyle changes to treat your condition.
- Moderate blockage (0.5 to 0.79). An ankle-brachial index number in this range shows that you have more significant blockage of your ankle and leg arteries. You may have noticed some pain in your legs or buttocks when you exercise.
- Severe blockage (less than 0.5). If your ankle-brachial index number is in this range, your leg arteries are significantly blocked and you may have pain in your legs even while resting. An ankle-brachial index of less than 0.4 suggests severe PAD.
- Rigid arteries (more than 1.4). If your ankle-brachial index number is higher than 1.4, this may mean that your arteries are rigid and don't compress when the blood pressure cuff is inflated. You may need an ultrasound test to check for peripheral artery disease instead of an ankle-brachial index test, or a toe-brachial index test, in which the blood pressures in your arm and big toe are compared.
The above numbers are based on guidelines Mayo Clinic uses. The guidelines suggested by the American Heart Association and the American College of Cardiology differ slightly. They suggest a normal ankle-brachial index ranges from 1.0 to 1.4, a borderline index ranges from 0.91 to 0.99, and an abnormal index is 0.9 or lower. If you have an exercise ankle-brachial index test, the ranges for results differ. Talk to your doctor about what your results mean.
Depending on the severity of your blockage, your doctor may recommend lifestyle changes, medications or surgery to treat PAD. Talk to your doctor about your options. You may also need additional imaging tests to see what treatment is best for you.
The test may not adequately measure the ankle-brachial index if you have severe diabetes or calcified arteries with significant blockage. Instead, your doctor may need to read your blood pressure at your big toe (toe-brachial index) to get an accurate test result if you have either of these conditions.
June 26, 2013
- Grenon SM, et al. Ankle-brachial index for assessment of peripheral artery disease. New England Journal of Medicine. 2009;361:e40.
- Ankle-brachial index. Vascular Disease Foundation. http://vasculardisease.org/peripheral-artery-disease/pad-diagnosis/ankle-brachial-index/. Accessed Sept. 18, 2012.
- AskMayoExpert. How are the results of ankle-brachial index testing classified at Mayo Clinic? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2012.
- Rooke TW, et al. 2011 ACCF/AHA focused update of the guideline for the management of patients with peripheral artery disease (updating the 2005 guideline): A report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines. Circulation. 2011;124:2020.
- Ankle Brachial Index Collaboration. Ankle brachial index combined with Framingham Risk Score to predict cardiovascular events and mortality: A meta-analysis. Journal of the American Medical Association. 2008;300:197.
- Grogan M (expert opinion). Mayo Clinic. Rochester, Minn. Aug. 24, 2012.