Diagnostics
ABI — Ankle-Brachial Index Testing
A simple, evidence-based bedside test that compares blood pressure at the ankle with blood pressure at the arm to screen for peripheral arterial disease and reduced circulation in the legs.
- Test time
- 10-20 minutes
- Radiation
- None
- Contrast
- Not required
- Results
- Same visit
What is the Ankle-Brachial Index?
The ankle-brachial index (ABI) is the ratio of the systolic blood pressure measured at the ankle to the systolic blood pressure measured at the arm. In healthy arteries these pressures are similar; when arteries in the legs are narrowed, ankle pressure falls and the ratio drops.
ABI is a long-established, guideline-supported screening test for peripheral arterial disease (PAD). It is quick, non-invasive and requires no contrast or radiation, which makes it well suited to routine cardiovascular and diabetic foot screening.
At MRC Healthcare, ABI results help our physicians decide whether circulation is a contributing factor in leg pain, slow-healing wounds or reduced walking tolerance — and whether further vascular imaging or specialist referral is warranted.
How the reading is taken and read
Blood pressure cuffs are placed on both arms and both ankles, and a hand-held Doppler probe is used to hear the pulse as each cuff deflates. The highest ankle pressure on each side is divided by the highest arm pressure to give the index for that leg.
A value close to 1.0 is normal. Lower values suggest narrowed leg arteries, and unusually high values can indicate stiff, calcified vessels — common in long-standing diabetes or kidney disease — which is why the result is always read together with your symptoms.
Both legs measured and compared side to side
Doppler used rather than a simple cuff reading for accuracy
Results interpreted against symptoms such as calf pain when walking
Repeatable, so it works well for monitoring over time
Ankle and arm pressures are compared to calculate the index for each leg.
Why it matters
Screens for PAD
Detects reduced arterial flow in the legs, often before symptoms become limiting.
Explains leg symptoms
Helps clarify calf pain on walking, coldness, numbness or slow-healing foot wounds.
Cardiovascular context
A low index is associated with wider cardiovascular risk and prompts broader assessment.
Fast and repeatable
Around 15 minutes, with no needles, contrast or radiation — easy to repeat at follow-up.
Who it may suit
Patients with diabetes, who are at higher risk of peripheral arterial disease
Smokers or former smokers, and patients with high blood pressure or high cholesterol
Anyone with cramping calf pain when walking that eases with rest
Patients with cold feet, non-healing foot wounds or reduced pulses
Patients over 50 seeking a baseline cardiovascular screening
What the test involves
Rest period
You lie flat and rest quietly for about 10 minutes so blood pressure readings are stable.
Arm measurement
Systolic pressure is measured in both arms using a cuff and a handheld Doppler probe.
Ankle measurement
Pressure is then measured at the posterior tibial and dorsalis pedis arteries in both ankles.
Index and review
The highest ankle pressure on each side is divided by the highest arm pressure, and your physician explains what the ratio means for you.
How to prepare
Before the test
Avoid caffeine, nicotine and strenuous exercise for a couple of hours beforehand, and wear loose clothing that allows access to both ankles and upper arms.
During the test
You rest flat for around ten minutes first, then lie still while each cuff is inflated in turn. The pressure is brief and there is no pain beyond mild tightness.
After the test
You can leave immediately. Your physician explains the index for each leg and whether ultrasound or vascular referral is advisable.
Important considerations
ABI is non-invasive and generally comfortable; cuff inflation causes brief pressure only.
Heavily calcified arteries — common in long-standing diabetes or kidney disease — can produce falsely high readings, so results are read alongside symptoms and other tests.
The test is not performed over an area with an open wound, recent surgery, or a known deep vein thrombosis.
An abnormal index is a reason for further assessment, not a diagnosis on its own.
Why ABI matters
- ABI is a widely used first-line screening test for peripheral arterial disease and is recommended where there are symptoms such as leg pain on walking, non-healing foot wounds or weak pulses.
- Reduced ABI is also a marker of wider cardiovascular risk, so an abnormal result usually prompts a broader review of blood pressure, lipids and glucose control.
- Falsely high readings occur when arteries are calcified; in those cases a toe-brachial index or duplex ultrasound is used instead.
- The test does not treat anything on its own — it directs the next step, whether that is risk-factor management, vascular imaging or specialist referral.
Frequently asked questions
Related care at MRC Healthcare
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Reviewed by MRC Healthcare Medical Team
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