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What You Need To Know About Ankle-Brachial Index (ABI)

Peripheral arterial disease (PAD) is a cardiovascular disorder characterized by a decrease in blood flow through the peripheral arteries, specifically those supplying the lower extremities. This decreased blood flow can result in claudication, which is typically described as pain or discomfort in the thigh or calf muscles during physical activity such as walking or exertion. PAD brings with it a significant impact on the quality of life and overall health outcomes of affected individuals.


According to the Centers for Disease Control and Prevention (CDC), PAD affects an estimated 6.5 million adults aged 40 and older in the United States. Its prevalence increases with age and among African American populations. PAD is also associated with other risk factors, such as smoking, high blood pressure, diabetes, and hyperlipidemia. Individuals diagnosed with PAD are at increased risk for the development of coronary artery disease and cerebrovascular disease. The presence of PAD serves as a marker for a heightened risk of subsequent cardiac and cerebrovascular events, not excluding myocardial infarction and stroke.


Diagnosing PAD early is crucial so that individuals may receive appropriate risk factor management and treatment to reduce the likelihood of these potentially life-threatening outcomes. One of the most widely used diagnostic tools for PAD is the ankle-brachial index (ABI). In this article, we will provide an overview of ABI as a diagnostic tool for PAD and its role in the management of this condition. We will also discuss the best practices for ABI testing in a clinical setting and the latest medical and interventional therapies for PAD.


Technical aspects of ABI testing

Traditionally, the ABI test is performed using a blood pressure cuff and a Doppler ultrasound device or stethoscope. The blood pressure cuff is used to measure the blood pressure at the ankle and arm. The Doppler ultrasound device or stethoscope is used to detect the blood flow in the arteries. The test is performed by taking the systolic blood pressure at the ankle and arm and then dividing the ankle pressure by the arm pressure. The measurement is typically taken on both arms and legs, and the higher value is used for the ABI calculation.

The results of the ABI test are reported as a ratio. A normal ABI is between 0.9 and 1.3. ABI values less than 0.9 are considered abnormal and are associated with PAD. However, it’s important to note that an abnormal ABI result does not necessarily mean the patient has PAD, and other diagnostic tests may be necessary to confirm this diagnosis.

PAD can lead to amputation and an increased risk of cardiovascular events if left untreated. Because it is simple, cost-effective, and non-invasive, ABI is advantageous in identifying asymptomatic individuals who are at risk of PAD. For patients who are already undergoing treatment for PAD, ABI can also be used to monitor the effectiveness of clinical interventions.

While ABI is widely used as a diagnostic tool, it is not without its limitations. Factors such as improper cuff placement, reduced blood flow, or the presence of arterial calcification may compromise the accuracy of the test results. Additionally, the ABI test only assesses blood flow to the lower extremities and, as such, may not detect the presence of PAD in other areas of the body. Therefore, it is crucial to take into account the patient’s reported symptoms and medical history when interpreting ABI test results. The ABI test should be used as part of an overall assessment of a patient and not as a standalone diagnostic tool.

Best practices for ABI testing

In order to ensure the accuracy of the ABI test results and the efficacy of the PAD diagnosis, physicians must provide clear and comprehensive instructions to patients. Specifically, patients should abstain from consuming caffeine and refrain from smoking for at least 30 minutes prior to the test, as these actions can elevate blood pressure and skew test results. Additionally, patients should be counseled to refrain from engaging in any physical activity that may cause an elevation in blood pressure, such as heavy lifting or strenuous exercise, for a minimum of 30 minutes prior to the test.

It is important to note that if a patient is taking any medications that may affect the results of the test, such as blood pressure or blood sugar medications, the physician should be informed in order to make any necessary adjustments or hold the medication for a certain period of time before the test.

During the test, the patient should be positioned in a supine position, and the extremities should be exposed for easy access. Next, a blood pressure cuff should be placed on the upper arm and inflated to a level of 20 to 30 mmHg above the last audible Korotkoff sound. The pressure should then be slowly released, and the pressure at which a Korotkoff sound is once again heard should be recorded as the systolic pressure at that specific location. The procedure ought to be repeated on the same side ankle, followed by the opposite leg, and then the opposite arm.

Applications of ABI

In the setting of suspected PAD, the ABI has been demonstrated to possess high diagnostic accuracy, with a sensitivity greater than 90% and a specificity greater than 95%.

The accuracy of ABI in identifying PAD in patients diagnosed with diabetes presenting with neuropathy or foot ulcers may be less accurate than other diagnostic methods. A normal ABI result in these patients should be taken cautiously, and imaging techniques may first be conducted before therapy is initiated.

In trauma patients, the use of ABI is limited to emergency use due to the widespread utilization of computed tomography angiography. In such patients, an ABI lower than 0.90 may indicate a need for further vascular imaging, such as angiography in stable patients or operative exploration in unstable patients.

Management of PAD

In the management of peripheral arterial disease (PAD), medical therapy is often the initial line of treatment. This typically includes the administration of medications such as cilostazol, pentoxifylline, and aspirin, which aim to improve blood flow and decrease the formation of clots. Additionally, statins and other cholesterol-lowering agents may be employed to reduce the risk of cardiovascular events.

For those with more severe cases of PAD, interventional therapy may be necessary. This can include techniques such as angioplasty, which involves the use of a small balloon to open narrowed or blocked arteries, or stenting, which involves the placement of a small metal mesh tube to keep the artery open. In more severe cases, surgical interventions such as bypass surgery may be required.

ABI is a useful tool for monitoring the response to treatment in patients with PAD. Prior to the initiation of treatment, ABI testing should be performed to establish a baseline measurement. Subsequent ABI measurements can then be used to evaluate the effectiveness of treatment. An increase in ABI value post-treatment indicates an improvement in blood flow, while a decrease in ABI value may indicate that the treatment was ineffective. Furthermore, monitoring ABI values over time can assist in identifying individuals who may be at a high risk of cardiovascular events and who may warrant more aggressive treatment.

Clinical benefits of TM FLOW in the care of PAD patients

TM Flow is a new diagnostic tool that can provide a simple to utilize ABI test. It combines ABI, autonomic nervous system (ANS), and sudomotor testing to evaluate PAD. The ANS test measures the function of both the sympathetic and parasympathetic branches of the ANS, which play a critical role in regulating the circulatory system. The sudomotor test, on the other hand, assesses the integrity of the small nerve fibers that control the sweat glands.

One of the main advantages of TM Flow over the traditional ABI test is that it can provide a more comprehensive evaluation of PAD. While ABI is a reliable test for PAD, it only purveys information about the blood flow in the lower extremities. It may also not be accurate in patients with severe PAD or in those with calcified arteries.

TM Flow, on the other hand, can provide a more detailed and accurate assessment of microvascular perfusion in the limbs, as it measures blood flow at the capillary level. This can help identify patients with PAD who suffer from a more severe disease or who are at substantial risk of complications. It also offers a more dynamic assessment of blood flow, as it can measure flow velocity and pressure fluctuations in real-time, allowing for a more comprehensive evaluation of the impact of various factors such as exercise and posture on blood flow. This can be particularly useful in catching early signs of PAD and in monitoring the effectiveness of treatments aimed at improving blood flow.

The best foot forward with the TM FLOW

If you’re looking for a combination ABI, SUDO motor, and ANS test for you patients, consider the TM Flow as a diagnostic testing option. This is a 15-minute test that a MA can perform with a quick, read-at-a-glance report generated as soon as the testing is complete. Visit our website or call us at 404-512-2475. We’d be happy to answer any of your questions you might have.


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