Ankle-brachial index (ABI) results: what the test involves and what the numbers mean
The ankle-brachial index (ABI) test is usually the first test used to diagnose peripheral artery disease (PAD). It compares the blood pressure in your ankle with the blood pressure in your arm. (NHLBI) The 2024 ACC/AHA guideline reports results as abnormal (0.90 or lower), borderline (0.91 to 0.99), normal (1.00 to 1.40) or noncompressible (above 1.40). (ACC/AHA, 2024)
What happens during the test
- Lying down: the ABI is calculated from the systolic blood pressure at the ankle divided by the systolic blood pressure at the arm (brachial artery) while you are lying down. (USPSTF, 2018)
- Cuffs and Doppler: the resting ABI is measured in each leg using a blood pressure cuff and a Doppler device to detect blood flow and pressure in the foot and arm arteries. It may be done in a vascular laboratory or in an office. (ACC/AHA, 2024) NHLBI describes it as a painless test. (NHLBI)
- How the number is worked out: for each leg, the higher of the two ankle artery pressures (dorsalis pedis and posterior tibial) is divided by the higher of the left and right arm pressures. (ACC/AHA, 2024)
- Exercise ABI: if you have leg symptoms on walking but your resting ABI is normal or borderline, ACC/AHA says an exercise treadmill ABI test should be done. (ACC/AHA, 2024) NHLBI says a drop of 20% or more in the ABI after exercise is abnormal. (NHLBI)
What the numbers mean
| Resting ABI | Reported as (ACC/AHA 2024) |
|---|---|
| 0.90 or lower | Abnormal (ACC/AHA, 2024) |
| 0.91 to 0.99 | Borderline (ACC/AHA, 2024) |
| 1.00 to 1.40 | Normal (ACC/AHA, 2024) |
| Above 1.40 | Noncompressible (ACC/AHA, 2024) |
- NHLBI wording: a healthy ABI result is 1.00 or greater. An ABI of less than 0.90 while resting may mean PAD, and an ABI of less than 0.40 is a sign of severe PAD. (NHLBI)
- Accuracy: in people with PAD symptoms, the resting ABI has a sensitivity of 69% to 79% and a specificity of 83% to 99% compared with imaging, although the sensitivity is reduced with diabetes. (ACC/AHA, 2024)
- Abnormal ABI without symptoms: people with an abnormal ABI and no symptoms have poorer cardiovascular illness and death outcomes than people with a normal ABI. (ACC/AHA, 2024)
Why diabetes can make results look falsely high
Noncompressible ankle arteries occur often with diabetes or chronic kidney disease and may give a falsely high ABI above 1.4 even when imaging confirms significant PAD. Toe arteries are rarely noncompressible, so a toe-brachial index (TBI) can be used instead: the toe (first digit) pressure divided by the higher of the two arm pressures. A TBI of 0.70 or lower is considered abnormal. ACC/AHA says a toe pressure or TBI with waveforms should be done when PAD is suspected and the resting ABI is above 1.40. (ACC/AHA, 2024) NHLBI says a TBI less than 0.7 is abnormal. (NHLBI) See the diabetic foot exam for the yearly foot check that can lead to this test.
Who doctors test
ACC/AHA recommends a resting ABI to diagnose PAD in people whose history or physical exam suggests it, such as leg symptoms on exertion. (ACC/AHA, 2024) It says screening with the resting ABI is reasonable for people at increased risk of PAD: (ACC/AHA, 2024)
- Age 65 or older.
- Age 50 to 64 with risk factors for atherosclerosis (for example diabetes, a history of smoking, dyslipidemia or high blood pressure), chronic kidney disease, or a family history of PAD.
- Under age 50 with diabetes and 1 other risk factor for atherosclerosis.
- Known atherosclerotic disease in another blood vessel bed (for example coronary, carotid or renal artery narrowing, or an abdominal aortic aneurysm).
For people without increased risk and without findings that suggest PAD, ACC/AHA does not recommend ABI screening; the yield in younger people without risk factors is low. (ACC/AHA, 2024) The USPSTF lists older age, diabetes, current smoking, high blood pressure, high cholesterol, obesity and physical inactivity as major risk factors, with current smoking and diabetes showing the strongest link. (USPSTF, 2018)
Possible harms
The USPSTF says the ABI test itself has minimal harms, but later harms are possible: false-positive and false-negative results, anxiety, labeling, and exposure to gadolinium or contrast dye from follow-up MRA or CT angiography. (USPSTF, 2018)
MedlinePlus, when to contact a medical professional. Contact your provider if you have: (MedlinePlus, PAD)
- A leg or foot that becomes cool to the touch, pale, blue, or numb
- Chest pain or shortness of breath with leg pain
- Leg pain that does not go away, even when you are not walking or moving (called rest pain)
- Legs that are red, hot, or swollen
- New sores/ulcers
- Signs of infection (fever, redness, general ill feeling)
- Symptoms of arteriosclerosis of the extremities
Where they differ:
- ACC/AHA (2024): screening with the resting ABI is reasonable for people at increased risk (all adults 65 or older, and younger adults with listed risk factors); not recommended for people without increased risk or signs of PAD. (ACC/AHA, 2024)
- USPSTF (2018): the evidence is insufficient to assess the balance of benefits and harms of ABI screening in adults without symptoms and without known PAD, heart disease or severe chronic kidney disease (I statement); an August 2023 literature scan found no new evidence to support an update. (USPSTF, 2018)
- MedlinePlus: there is no screening test recommended to identify PAD in people without symptoms. (MedlinePlus, PAD)
- Cutoffs: ACC/AHA uses 0.90 or lower for abnormal and names a borderline band of 0.91 to 0.99; NHLBI says less than 0.90 may mean PAD and adds less than 0.40 as a sign of severe PAD. ACC/AHA calls a TBI of 0.70 or lower abnormal; NHLBI says less than 0.7. (ACC/AHA, 2024)(NHLBI)
Your doctor decides what your result means for you.
This page does not give treatment advice. If you have an abnormal result, see after an abnormal screening result for questions to ask.
Questions people ask
What is a normal ankle-brachial index?
The 2024 ACC/AHA guideline says a resting ABI should be reported as abnormal at 0.90 or lower, borderline at 0.91 to 0.99, normal at 1.00 to 1.40, and noncompressible above 1.40. NHLBI says a healthy ABI is 1.00 or greater. (ACC/AHA, 2024) (NHLBI)
What does an ABI above 1.40 mean?
It means the ankle arteries could not be compressed by the cuff. ACC/AHA says this happens often with diabetes or chronic kidney disease and can give a falsely high ABI even when imaging confirms significant PAD, so a toe-brachial index should be done when PAD is suspected. (ACC/AHA, 2024)
Who should have an ABI test?
ACC/AHA recommends a resting ABI for people whose history or exam suggests PAD, and says screening with the ABI is reasonable for people at increased risk, such as everyone 65 or older and people 50 to 64 with risk factors like diabetes or smoking. It does not recommend it for people without increased risk or signs. (ACC/AHA, 2024)
Does the USPSTF recommend ABI screening?
No recommendation either way. The USPSTF found the evidence insufficient to assess the benefits and harms of screening for PAD with the ABI in adults without symptoms (an I statement, 2018). (USPSTF, 2018)
Does the ABI test hurt?
NHLBI describes it as a painless test using a blood pressure cuff and an ultrasound device. ACC/AHA calls it noninvasive, simple, and with minimal risks. (NHLBI) (ACC/AHA, 2024)