Ankle Brachial Index
The Ankle-Brachial Index (ABI) is a simple, non-invasive test that compares blood pressure in the ankle to the arm — the primary screening tool for peripheral artery disease (PAD) and an independent cardiovascular risk marker.
Ankle-Brachial Index (ABI) testing measures blood flow to the legs to detect peripheral artery disease early and guide treatment
The Ankle-Brachial Index is the standard non-invasive test for detecting peripheral artery disease (PAD) — comparing systolic blood pressure at the ankle to the brachial artery pressure at the arm. A reduced ABI indicates impaired arterial perfusion to the lower limbs and confirms the presence of haemodynamically significant arterial disease. Beyond PAD diagnosis, a low ABI is an independent predictor of cardiovascular events — patients with an ABI below 0.9 carry a two- to threefold increased risk of myocardial infarction and stroke regardless of symptoms.
How the Test Is Performed
The ABI is performed with the patient supine after five minutes of rest. Blood pressure cuffs are applied to both arms and both ankles, and a handheld Doppler probe is used to detect flow signals at the brachial, posterior tibial, and dorsalis pedis arteries. The ABI is calculated by dividing the higher ankle systolic pressure by the higher brachial systolic pressure for each leg. The test is painless, requires no preparation, and takes approximately 15 minutes. No downtime is required.
Interpreting ABI Results
ABI Value Interpretation
Above 1.40: Non-compressible vessels — calcified arteries (diabetes, CKD); requires toe-brachial index (TBI)
1.00 – 1.40: Normal arterial perfusion
0.91 – 0.99: Borderline — early or mild reduction in perfusion
0.41 – 0.90: Mild to moderate PAD
0.40 and below: Severe PAD — high risk of critical limb ischaemia, ulceration, and limb loss
An ABI above 1.40 indicates non-compressible, calcified vessels — common in longstanding diabetes and chronic kidney disease — where ankle pressures are falsely elevated. In these patients, the toe-brachial index (TBI) — measuring digital artery pressure at the toe — provides a more reliable assessment of true perfusion.
Exercise ABI
When resting ABI is borderline or normal but symptoms strongly suggest exertional PAD, an exercise ABI is performed — measuring ankle pressures immediately after treadmill walking. In healthy arteries, exercise maintains or increases ankle pressure. In PAD, perfusion fails to meet increased demand and ankle pressures drop significantly post-exercise, unmasking haemodynamically significant disease not detectable at rest. Exercise ABI improves diagnostic sensitivity for mild PAD and objectively quantifies functional walking impairment.
Who Should Have an ABI Test
ABI screening is recommended for patients over 65, patients over 50 with diabetes or a smoking history, patients of any age with symptoms of claudication or rest pain, patients with non-healing foot wounds or ulcers, and patients with established cardiovascular disease — coronary artery disease, stroke, or carotid disease — in whom PAD frequently coexists. Diabetic patients with peripheral neuropathy may have advanced PAD without classical symptoms, making screening particularly important in this group.
What Happens After the Test
Results are interpreted in the context of symptoms, cardiovascular risk factors, and clinical findings. A normal ABI with typical claudication symptoms may prompt exercise ABI testing. An abnormal ABI initiates a structured management pathway — cardiovascular risk factor optimisation, antiplatelet therapy, supervised exercise programme, and arterial duplex ultrasound or CT angiography for anatomical mapping where intervention is being considered. Patients with an ABI below 0.4 or features of critical limb ischaemia are referred for urgent vascular assessment and revascularisation planning.
Concerned about leg circulation, claudication, or non-healing wounds? An ABI test at Dr. Peter Chang's clinic at Paragon Medical Centre, Orchard Road takes 15 minutes and can identify arterial disease before serious complications develop. Book today.