The ABI Test

The ABI test is one of several tests used to determine whether or not peripheral artery disease (PAD) is present. It can be performed on a regular basis to assess quickly whether plaque build-up in the leg arteries, known as PAD, is getting worse. Knowing and tracking the ABI number is important for patients and physicians as they determine the best treatment approach. In addition to guiding treatment and whether an intervention might be warranted, the ABI can predict the severity of PAD and the risk of future leg problems, including leg rest pain, poor healing of foot wounds or amputation. It also can predict the risk of future problems from atherosclerosis in other parts of the body, such as heart attack and stroke.

ABI is a simple and non-invasive test. Blood pressure measurements are taken at the arms and ankles using a pencil-shaped ultrasound device called a Doppler. A Doppler instrument produces sound waves (not x-rays) and is considered noninvasive because it does not require the use of needles or catheters. The ABI test can be performed in a doctor's office or vascular laboratory.

Similar to a cholesterol or blood pressure test, the ABI provides a number. PAD experts are advising people over the age of 50 to “Know Your ABI” to ensure early detection and optimum treatment of the disease.

How is the exam given?

The patient lies down and standard blood pressure cuffs are placed around both ankles and arms. These cuffs are inflated briefly above the patient’s normal systolic blood pressure. Once the cuffs are deflated, blood pressure measurements are taken. The arm and ankle systolic blood pressure measurements are recorded. Then the ankle systolic pressures are divided by the highest arm pressure to establish an ABI measurement for each leg.

The ABI range that is generally considered normal is .91 to 1.3. Lower ABI values are associated with a higher risk. Traditional diagnostic criteria for PAD based on the ABI are interpreted as follows:¹⁰

• .91 to 1.3 = normal
• .7 to .9 = mild obstruction
• .4 to .69 = moderate obstruction
• less than .4 = severe obstruction

What Do the ABI Results Mean?*

An ABI value greater than .8 is rarely associated with short-term leg problems such as foot wounds or amputation. Nevertheless, any evidence of PAD (where the ABI measurement is less than 1 can be associated with future risk of heart attack and/or stroke, or potentially PAD.

An ABI value between .4 and .8 is moderately decreased and such patients often experience some symptoms such as pain in the legs. Attention to foot care is extremely important to prevent accidental injury or infection. Again, any evidence of PAD is associated with future risk of heart attack and/or stroke. Serious efforts to keep the patient’s risk factors under control are essential to keep PAD from getting worse.

An ABI value of less than .4 indicates severe PAD. Patients should be extremely careful to avoid any foot injuries. Proper foot care may prevent development of non-healing wounds, rest pain, or even gangrene. Usually, care from a vascular specialist is required. The specialist will evaluate the risk and benefits to improve leg blood flow through surgery or other interventions like plaque excision.

How reliable is this exam?

Although the ABI is extremely reliable and approaches 95 percent accuracy in detecting PAD, this test may not be accurate in all patients.¹¹ A normal ABI value does not absolutely rule out the possibility of PAD for a few individuals. Some patients with a normal or near-normal ABI results may have symptoms suggesting PAD. A treadmill exercise or reactive hyperemia test may be recommended to test further for the disease and the cause of pain.

Some patients with long-standing diabetes, kidney disease, or some elderly patients, may have rigid blood vessels. These may be difficult to compress with the blood pressure cuff and, in these patients, the ABI reading may not be accurate.

What other exams will work?

When an ABI does indicate PAD, the patient generally will undergo angiography to confirm a diagnosis. This minimally invasive procedure involves injecting a dye into the arteries and reviewing the area by X-ray. Typically, the physician can see the blockage on the angiogram images.

1. American Diabetes Association, Peripheral Arterial Disease in People with Diabetes, “Diabetes Care,” 26(12):3333-3341, 2003
2. Becker GJ, et al. The importance of increasing public and physician awareness of peripheral arterial disease. J Vasc Interv Radiol 2002; 13[1]:7–11
3. American Diabetes Association
4. “ACC/AHA 2005 Practice Guidelines for the Management of Patients With Peripheral Arterial Disease”, Alan T. Hirsch, MD et al. Circulation 2006; 113; 463-654
5. U.S. Census Bureau Middle Series Projections and The Sage Group Estimates
6. “Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II)” , L. Norgren et al. Eur J Vasc Endovasc Surg 33, S1-S70 (2007)
7. TASC Epidemiology.S10-15
8. “ACC/AHA 2005 Practice Guidelines for the Management of Patients With Peripheral Arterial Disease”, Alan T. Hirsch, MD et al. Circulation 2006; 113; 463-654
9. American Diabetes Association, Peripheral Arterial Disease in People with Diabetes, Diabetes Care 26(12):3333-3341, 2003.
10. Vascular Disease Foundation