At Alliance Foot & Ankle Specialists, we often conduct Ankle Brachial Index (ABI) and Toe Brachial Index (TBI) testing during routine visits. These simple, non-invasive tests can tell us a great deal about your overall foot health and help us check for red flags that could point to serious issues that need immediate attention.
These two essential diagnostic tools play a crucial role in evaluating peripheral vascular foot health and provide invaluable data about the circulation of blood to the extremities. This information helps us detect and manage conditions such as peripheral artery disease (PAD) and diabetes-related foot complications.
Our Keller podiatrist discusses the ABI and TBI tests, why they matter, how they are used, and what patients can expect during these tests, as well as the reasons our team takes the results so seriously. 
The Ankle Brachial Index (ABI)
The ABI is a non-invasive and painless diagnostic test used to assess the blood flow and circulation in the lower limbs, particularly in the feet. It is a ratio of the systolic blood pressure measured at the ankle to that measured at the brachial artery in the arm.
The ABI is calculated by dividing the highest ankle systolic pressure by the highest brachial (arm) systolic pressure. More simply, a medical professional uses a blood pressure cuff on your arm and your ankle and compares the numbers.
An ABI reading less than 0.90 generally indicates peripheral artery disease (PAD), a condition characterized by the narrowing or blockage of arteries in the legs, resulting in reduced blood flow. PAD can lead to leg pain, ulcers, and even limb-threatening ischemia if left untreated. Our doctors will use your ABI score to assess whether or not you might suffer from PAD and how severe it is—and from that, we can form a comprehensive treatment plan.
The Toe Brachial Index (TBI)
TBI, sometimes referred to as the Toe Brachial Pressure Index (TBPI), is an extension of the ABI. While the ABI focuses on the blood pressure in the ankle, the TBI measures the blood pressure in the toes. The TBI is particularly useful when ABI measurements are inconclusive due to factors such as arterial calcification, non-compressible vessels, or anatomical variations. It can provide a more accurate assessment of peripheral vascular health in such cases.
To calculate the TBI, the highest systolic pressure at the toes is divided by the highest brachial systolic pressure, similar to the ABI. A TBI reading less than 0.70 is typically considered abnormal and may indicate significant vascular compromise in the lower extremities. This can be crucial in identifying severe PAD and determining the urgency of needed intervention.
At Alliance Foot & Ankle Specialists, we may take your TBI if it’s difficult to measure your ABI, or simply in addition to your ABI test.
Why Podiatrists Use These Tests
These two small numbers can give our podiatrists crucial information about the health of a patient’s feet. And we can use those numbers to inform every step of our care. More specifically, ABI and TBI help us in three major ways:
Early Detection of PAD
ABI and TBI tests are essential tools for detecting PAD, a condition we see often in podiatric patients. Early diagnosis allows us to implement interventions, suggest lifestyle modifications, and prescribe medications to slow down the progression of the disease and reduce the risk of complications. Getting PAD diagnosed and treated early can greatly increase the quality of your life.
Risk Assessment
ABI and TBI tests provide a quantitative assessment of a patient's vascular health. This information is invaluable in assessing the risk of developing diabetic foot ulcers, infections, and other complications in individuals with diabetes, as well as in those with a history of smoking or cardiovascular diseases. Being aware of these risks is a huge step toward preventing them.
Treatment Guidance
The results of ABI and TBI tests help podiatrists determine the appropriate course of treatment. In cases of severe PAD, this may involve referring patients for vascular intervention or surgical procedures to restore blood flow to the affected limb. When it comes to risk assessment, these tests can let our podiatrists know how to educate and inform the patient about issues like common diabetic foot problems.
What to Expect During ABI and TBI Tests
We understand that any new medical tests can be intimidating and even scary. Here’s how a typical ABI or TBI test is administered:
Before the Test
Before the test, patients should wear comfortable clothing, as the tests are typically conducted with the patient lying down. It’s essential to inform your doctor of any medical conditions or medications that may affect blood pressure and provide any other health information that could affect the test or the interpretation of results.
During the Test
During the test, a blood pressure cuff is wrapped around the arm and ankle (for ABI) or toes (for TBI). A Doppler ultrasound device may be used to detect the blood pressure signals in the arteries.
Using the cuffs, systolic blood pressure is recorded at the brachial artery and the ankle or toe arteries. Multiple measurements are taken at different locations to ensure accuracy.
Next, your doctor will calculate the ABI or TBI by dividing the highest systolic pressure at the ankle or toe by the highest brachial systolic pressure. Based on the calculated values, he will determine whether the patient has normal circulation or if further evaluation or treatment is needed.
After the Test
After the conclusion of the test, our doctor will communicate the results to you and explain their meaning. They will discuss a treatment plan and all necessary next steps.
The Advantages of ABI and TBI Tests
ABI and TBI tests are incredibly helpful and important to both podiatrists and patients for many reasons, including:
They’re Non-Invasive
Both ABI and TBI tests are non-invasive, making them safe and painless for patients. There is no need for needles or contrast agents, and the tests can be done quickly and economically.
They Promote Early Detection
These tests enable the early detection of vascular issues, allowing for timely intervention and reducing the risk of severe complications.
They Are an Objective Assessment
ABI and TBI tests provide objective measurements, reducing the risk of subjectivity in diagnosis and treatment decisions.
They’re Cost-Effective
These tests are cost-effective compared to more invasive diagnostic procedures, making them accessible to a broader range of patients.
They Improve Patient Outcomes
By identifying vascular issues early and guiding appropriate treatment, ABI and TBI tests can help improve patient outcomes, reduce amputation rates, and enhance quality of life.
Smart ABI/TBI and Sudomotor Test
At Alliance Foot & Ankle Specialists, we offer a Smart ABI/TBI and Sudomotor Test that makes ABI and TBI testing even faster and easier—with added accuracy.
The Smart-LEDA Plus solution offers our team the ability to perform rapid non-invasive arterial studies and sudomotor function tests with the added accuracy of TBI and microvascular data. Sudomotor function testing is an additional tool for diagnosing peripheral autonomic neuropathy.
ABI and TBI Tests: Promoting Overall Health
ABI and TBI tests are indispensable tools to screen our patients, guide treatment decisions, and monitor the effectiveness of interventions. Understanding both types of tests is crucial for us to provide comprehensive, compassionate, and thoughtful care to our patients.