Measuring Foot and Ankle Disability Index

The ankle-brachial index (ABI) measurement, also referred to as the ankle-brachial pressure index, is a rapid, non-invasive, and painless diagnostic vascular test. This method compares systolic blood pressure measured in the upper extremities (brachial arteries) with systolic blood pressure measured in the lower extremities (ankle level) to detect peripheral artery disease (PAD) and assess overall cardiovascular risk.

What is the ankle-brachial index (ABI)?

In a healthy individual resting in a supine position, blood pressure at the ankle is typically equal to or slightly higher than brachial blood pressure. The ankle-brachial index is a mathematical ratio calculated by dividing the highest systolic blood pressure measured at the ankle by the highest systolic blood pressure measured in either arm.

When atherosclerotic plaques develop within the arteries of the lower limbs, the vascular lumen narrows or occludes, leading to a decrease in perfusion pressure in the distal extremity (foot and ankle region). The ABI test, performed using pneumatic pressure cuffs paired with a continuous-wave Doppler ultrasound probe or automated oscillometric systems, enables detection of early, asymptomatic arterial stenoses as well as advanced disease.

When is an ankle-brachial index measurement performed?

An ABI measurement is indicated for the following clinical symptoms and risk factors:

• leg pain during walking (intermittent claudication): when aching, cramping, fatigue, or discomfort develops in the calves, thighs, or buttocks during exertion and resolves with rest;
• signs of lower-extremity circulatory insufficiency: cold feet, numbness, skin pallor, cyanosis, delayed nail growth, or hair loss on the lower legs;
• chronic non-healing wounds or tissue loss: trophic ulcers, diabetic foot syndrome, or suspected ischemic gangrene;
• diabetes mellitus: in patients with diabetes duration exceeding 10 years or with concomitant vascular risk factors;
• elevated cardiovascular risk profiles: individuals aged 65 years and older, smokers aged 50 years and older, or patients with arterial hypertension, dyslipidemia, and hypercholesterolemia;
• established atherosclerotic disease in other vascular beds: patients with documented coronary artery disease, history of myocardial infarction, ischemic stroke, or carotid artery stenosis;
• post-revascularization monitoring: assessing bypass graft patency or in-stent hemodynamics following angioplasty or surgical interventions.

Procedure flow and preparation

The test is performed in a dedicated vascular diagnostics room or vascular surgery outpatient clinic. The procedure takes approximately 15 to 20 minutes.

Procedure steps:

• resting phase: the patient lies flat in a supine position and rests quietly for 5 to 10 minutes to allow systemic hemodynamic parameters to stabilize;
• cuff placement: standard pneumatic blood pressure cuffs are wrapped around both upper arms (above the antecubital fossa) and around both lower legs (above the malleoli);
• Doppler pressure registration: using a Doppler ultrasound probe, flow signals are identified in the brachial arteries, dorsalis pedis arteries, and posterior tibial arteries; cuffs are inflated until flow signals disappear and are slowly deflated to detect the return of the first arterial pulse signal;
• index calculation: the ABI is calculated individually for each leg using the higher of the two ankle pressures divided by the highest arm pressure.

Preparation requirements:

• abstaining from smoking for at least 1 to 2 hours prior to the test, as nicotine induces peripheral vasoconstriction;
• refraining from caffeinated beverages for at least 1 to 2 hours;
• wearing loose, comfortable clothing that allows easy exposure of arms and lower legs;
• continuing daily prescribed medications unless specific withholding instructions have been given by the attending physician.

Interpretation of results

Calculated ABI values categorize the presence and severity of lower-extremity peripheral artery disease:

• ABI between 1.00 and 1.40 (normal): indicates normal arterial perfusion in the lower extremities;
• ABI between 0.91 and 0.99 (borderline): indicates possible early arterial compromise warranting clinical monitoring;
• ABI between 0.71 and 0.90 (mild PAD): reflects mild arterial stenosis, often associated with mild intermittent claudication;
• ABI between 0.41 and 0.70 (moderate PAD): reflects significant arterial obstruction, typically causing distinct claudication after short walking distances;
• ABI equal to or less than 0.40 (severe PAD): indicates critical limb-threatening ischemia, characterized by ischemic rest pain and high risk of tissue necrosis;
• ABI greater than 1.40 (non-compressible calcified vessels): indicates medial arterial calcification (Mönckeberg's arteriosclerosis), frequently encountered in advanced diabetes or end-stage renal disease, requiring alternative diagnostic methods (such as the toe-brachial index).

The obtained diagnostic parameters enable physicians to initiate targeted medical therapy or refer the patient for specialized vascular surgical evaluation.