What is Ankle-Brachial Index? Purpose, Levels/Procedure & Results

The ankle-brachial index (ABI) is a simple, painless test that compares blood pressure in your ankle to blood pressure in your arm. This quick measurement helps doctors detect peripheral artery disease (PAD), a condition where narrowed arteries reduce blood flow to your legs and feet.

Think of it as a health check for your circulation. When blood flows freely through healthy arteries, the pressure readings between your ankle and arm should be fairly similar. If there's a significant difference, it might signal that your leg arteries aren't getting the blood flow they need.

What is ankle-brachial index?

The ankle-brachial index is a ratio that compares the blood pressure in your ankle to the blood pressure in your arm. Your doctor calculates this by dividing your ankle pressure by your arm pressure, giving you a number that reflects how well blood flows to your lower extremities.

A normal ABI reading typically falls between 0.9 and 1.3. This means the blood pressure in your ankle is about 90% to 130% of the pressure in your arm. When this ratio drops below 0.9, it suggests your leg arteries might be narrowed or blocked, which could indicate peripheral artery disease.

The test is incredibly straightforward and takes just a few minutes to complete. You won't need any special preparation, and there's no discomfort involved. It's one of the most reliable screening tools doctors have for catching circulation problems early.

Why is ankle-brachial index done?

Doctors use the ankle-brachial index primarily to screen for peripheral artery disease, a condition that affects millions of people worldwide. PAD occurs when fatty deposits build up in your leg arteries, reducing blood flow to your feet and legs.

Early detection matters because PAD often develops silently without obvious symptoms. Many people don't realize they have circulation problems until the condition has progressed significantly. The ABI test can catch these issues before they become serious health concerns.

Your doctor might recommend this test if you have risk factors for artery disease. These include diabetes, high blood pressure, high cholesterol, smoking history, or being over 65 years old. The test is also useful if you're experiencing leg pain when walking, slow-healing wounds on your feet, or coldness in your lower legs.

Beyond screening, the ABI helps doctors monitor existing peripheral artery disease and evaluate how well treatments are working. It's also valuable for assessing your overall cardiovascular risk, since PAD often indicates similar problems in other arteries throughout your body.

What is the procedure for ankle-brachial index?

The ankle-brachial index procedure is remarkably simple and takes about 10 to 15 minutes to complete. You'll lie comfortably on an examination table while your healthcare provider measures blood pressure in both your arms and ankles using a standard blood pressure cuff and a special ultrasound device called a Doppler.

Here's what happens during your test:

1. You'll remove your shoes and socks and lie flat on your back
2. Your provider places blood pressure cuffs on both arms and both ankles
3. They apply ultrasound gel to your skin where they'll check for pulses
4. Using a Doppler device, they locate the pulse in your arm and inflate the cuff
5. They slowly release the pressure while listening for when blood flow returns
6. The same process is repeated for each ankle, checking pulses in your feet
7. Your provider calculates the ratio by dividing ankle pressure by arm pressure

The Doppler device amplifies the sound of blood flowing through your arteries, making it easy for your provider to detect even weak pulses. You might hear whooshing sounds during the test, which is completely normal and just the sound of your blood flow being amplified.

The procedure is entirely painless. You'll feel the familiar sensation of a blood pressure cuff inflating and deflating, but nothing more uncomfortable than a routine blood pressure check. Most people find the test quite relaxing.

How to prepare for your ankle-brachial index?

The wonderful thing about the ankle-brachial index test is that it requires virtually no preparation on your part. You can eat normally, take your regular medications, and go about your usual activities before the appointment.

There are just a few simple things to keep in mind to make your test go smoothly:

• Wear loose, comfortable clothing that allows easy access to your arms and legs
• Avoid tight socks or stockings that might leave marks on your ankles
• Try to rest for at least 5 minutes before the test to ensure accurate readings
• Let your provider know about any medications you're taking, especially blood thinners
• Mention if you have any skin conditions or injuries on your arms or legs

If you're a smoker, try to avoid smoking for at least 30 minutes before your test, as nicotine can temporarily affect your blood pressure readings. Similarly, if you've just exercised vigorously, let your provider know so they can allow extra time for your circulation to return to its resting state.

Most importantly, don't worry about the test results beforehand. The ABI is a screening tool, and if any issues are detected, your healthcare team will work with you to address them. Remember, early detection of circulation problems gives you the best opportunity for effective treatment.

How to read your ankle-brachial index?

Understanding your ankle-brachial index results is straightforward once you know what the numbers mean. Your result will be expressed as a decimal number, typically ranging from 0.4 to 1.4, which represents the ratio between your ankle and arm blood pressures.

Here's how to interpret your ABI results:

• 1.0 to 1.3: Normal circulation with healthy blood flow to your legs
• 0.9 to 0.99: Borderline, suggesting mild narrowing that warrants monitoring
• 0.8 to 0.89: Mild peripheral artery disease with some circulation compromise
• 0.5 to 0.79: Moderate PAD requiring medical attention and lifestyle changes
• Less than 0.5: Severe PAD needing immediate medical evaluation
• Above 1.3: May indicate stiff arteries, often seen in diabetes or kidney disease

A normal ABI doesn't necessarily mean your arteries are perfect, but it does indicate that blood flow to your legs is adequate. If your reading is borderline or abnormal, don't panic. Many people with mild PAD live normal, active lives with proper management.

Your doctor will consider your ABI results alongside your symptoms, medical history, and risk factors to determine if additional testing or treatment is needed. Sometimes, slight variations in readings can occur due to factors like room temperature or recent physical activity, so your provider might recommend repeating the test to confirm results.

How to fix your ankle-brachial index?

Improving your ankle-brachial index focuses on enhancing blood flow to your legs and preventing further artery narrowing. The good news is that many people can significantly improve their circulation through lifestyle changes and, when necessary, medical treatments.

Lifestyle modifications form the foundation of improving your ABI and overall vascular health:

• Exercise regularly: Walking programs specifically help develop collateral circulation around blocked arteries
• Quit smoking: Smoking cessation is the single most important step for improving circulation
• Manage diabetes: Keep blood sugar levels well-controlled to prevent further artery damage
• Control blood pressure: Maintain readings below 130/80 mmHg through diet, exercise, and medication if needed
• Lower cholesterol: Reduce LDL cholesterol to slow plaque buildup in arteries
• Maintain healthy weight: Excess weight puts additional strain on your circulatory system

Medical treatments may be necessary for more significant circulation problems. Your doctor might prescribe medications to improve blood flow, prevent blood clots, or manage underlying conditions like diabetes and high blood pressure. In some cases, procedures like angioplasty or bypass surgery might be recommended to restore blood flow.

The key is working closely with your healthcare team to develop a comprehensive plan tailored to your specific situation. Many people see meaningful improvements in their ABI within months of making consistent lifestyle changes, especially with regular exercise and smoking cessation.

What is the best ankle-brachial index?

The ideal ankle-brachial index falls between 1.0 and 1.2, indicating that blood pressure in your ankle is nearly equal to or slightly higher than the pressure in your arm. This range suggests excellent circulation with no significant blockages in your leg arteries.

An ABI of 1.0 means your ankle pressure equals your arm pressure, which is perfectly normal and healthy. Readings between 1.0 and 1.2 are considered optimal because they indicate good blood flow without suggesting overly stiff arteries.

While readings up to 1.3 are still considered normal, consistently high values above 1.3 might indicate that your arteries have become stiff or calcified. This condition, called medial sclerosis, is more common in people with diabetes or chronic kidney disease. Stiff arteries can make ABI readings less reliable for detecting blockages.

It's worth noting that the "best" ABI for you depends on your individual circumstances, age, and health conditions. Your doctor will interpret your results in the context of your overall health picture, not just as an isolated number. The goal is maintaining adequate circulation to keep your legs and feet healthy and functional.

What are the risk factors for low ankle-brachial index?

Several factors can increase your likelihood of developing a low ankle-brachial index, which typically indicates peripheral artery disease. Understanding these risk factors helps you take proactive steps to protect your circulation and overall cardiovascular health.

The most significant risk factors include conditions and lifestyle choices that damage your arteries over time:

• Smoking: Tobacco use dramatically increases your risk and accelerates artery narrowing
• Diabetes: High blood sugar damages blood vessels and increases PAD risk by 2-4 times
• High blood pressure: Chronic hypertension puts extra strain on artery walls
• High cholesterol: Elevated LDL cholesterol contributes toxic plaque buildup
• Age over 65: Arteries naturally become less flexible and more prone to narrowing with age
• Family history: Genetic factors can predispose you to cardiovascular disease
• Obesity: Excess weight increases inflammation and strain on your circulatory system
• Sedentary lifestyle: Lack of physical activity contributes to poor circulation

Some less common but important risk factors include chronic kidney disease, inflammatory conditions like rheumatoid arthritis, and a history of heart disease or stroke. African Americans and people with Hispanic heritage also face higher risks for developing peripheral artery disease.

The more risk factors you have, the greater your likelihood of developing circulation problems. However, many of these factors are modifiable through lifestyle changes and proper medical management, giving you significant control over your vascular health.

Is it better to have high or low ankle-brachial index?

Neither extremely high nor low ankle-brachial index readings are ideal. The goal is to have an ABI in the normal range of 0.9 to 1.3, which indicates healthy circulation without artery stiffness or blockages.

A low ABI (below 0.9) suggests that your leg arteries are narrowed or blocked, reducing blood flow to your feet and legs. This condition, known as peripheral artery disease, can lead to serious complications if left untreated. Low readings are definitely concerning and require medical attention.

On the other hand, a high ABI (above 1.3) isn't necessarily better. Elevated readings often indicate that your arteries have become stiff or calcified, which can happen with diabetes, kidney disease, or advanced age. Stiff arteries can't compress properly during the test, leading to falsely high readings that don't accurately reflect your true circulation status.

When your ABI is too high, your doctor might need additional tests like toe-brachial index or pulse volume recordings to get a more accurate picture of your circulation. Very high readings can also indicate increased cardiovascular risk, even if your leg circulation appears adequate.

The sweet spot is maintaining an ABI between 1.0 and 1.2, which suggests optimal circulation with healthy, flexible arteries. This range indicates that your heart is effectively pumping blood to your legs without encountering significant resistance from narrowed or stiffened arteries.

What are the possible complications of low ankle-brachial index?

A low ankle-brachial index indicates reduced blood flow to your legs and feet, which can lead to several serious complications if not properly managed. Understanding these potential problems helps motivate lifestyle changes and medical treatment that can prevent or minimize these issues.

The most common complications of poor leg circulation develop gradually and may worsen over time:

• Leg pain while walking (claudication): Muscles don't get enough oxygen during activity, causing cramping or aching
• Slow wound healing: Cuts, sores, or injuries on your feet and legs take much longer to heal
• Skin changes: Your legs might become pale, blue, or develop a shiny appearance
• Hair loss: Reduced circulation can cause hair to stop growing on your legs and feet
• Nail problems: Toenails may become thick, brittle, or grow slowly
• Temperature sensitivity: Your feet and legs may feel constantly cold

More serious complications can develop in severe cases where circulation is significantly compromised. These include persistent pain even at rest, non-healing ulcers or sores, and in rare cases, tissue death (gangrene) that might require amputation.

People with low ABI also face increased risk of heart attack and stroke because the same disease process affecting leg arteries often affects coronary and brain arteries. However, with proper medical care and lifestyle modifications, most people with PAD can prevent these serious complications and maintain good quality of life.

What are the possible complications of high ankle-brachial index?

While a high ankle-brachial index might seem preferable to a low one, readings above 1.3 can indicate arterial stiffness that brings its own set of potential complications. These issues are often related to the underlying conditions that cause artery stiffening rather than the high ABI itself.

High ABI readings most commonly occur in people with diabetes, chronic kidney disease, or advanced age, and the complications often reflect these underlying conditions:

• Masked circulation problems: Stiff arteries may hide true blockages, making it harder to detect PAD
• Increased cardiovascular risk: Arterial stiffness often indicates widespread vascular disease
• Poor wound healing: Despite normal-appearing circulation, tissue healing may still be compromised
• Diabetic complications: High ABI in diabetes often signals advanced microvascular disease
• Kidney-related issues: Arterial stiffness can worsen kidney function over time

The main concern with high ABI is that it can provide false reassurance about your circulation status. Your doctor might need additional tests to get an accurate picture of blood flow to your legs and feet. These might include toe-brachial index measurements or more sophisticated imaging studies.

People with consistently high ABI readings need careful monitoring for cardiovascular disease and may require more aggressive management of underlying conditions like diabetes or kidney disease. The goal is preventing the progression of arterial stiffness while ensuring adequate blood flow to your extremities.

When should I see a doctor for ankle-brachial index?

You should consider getting an ankle-brachial index test if you have risk factors for peripheral artery disease or are experiencing symptoms that might indicate circulation problems. Early detection and treatment can prevent serious complications and improve your quality of life.

Several situations warrant discussion with your doctor about ABI testing:

• Age over 65: Routine screening is recommended regardless of symptoms
• Leg pain with walking: Cramping, aching, or fatigue in your legs during activity
• Slow-healing wounds: Cuts or sores on your feet or legs that don't heal within normal timeframes
• Risk factor presence: Diabetes, smoking, high blood pressure, or high cholesterol
• Family history: Close relatives with peripheral artery disease or cardiovascular disease
• Foot problems: Cold feet, color changes, or decreased pulse in your feet

You should seek immediate medical attention if you experience severe leg pain at rest, open sores that won't heal, or any signs of infection in wounds on your feet or legs. These symptoms might indicate advanced circulation problems requiring urgent treatment.

If you've already had an ABI test and your results were abnormal, follow your doctor's recommendations for monitoring and follow-up testing. Regular check-ups help track changes in your circulation and adjust treatment as needed.

Don't wait for symptoms to become severe before seeking evaluation. Many people with early peripheral artery disease have no symptoms at all, making screening tests like the ABI especially valuable for early detection and prevention.