Background

The ankle-brachial index (ABI) is a noninvasive measurement test which compares upper and lower limbs blood pressure level.

ABI detects resistance to blood flow in lower extremities due to arterial narrowing from atherosclerosis.

ABI measurement simplicity and low cost make it an effective test for early peripheral arterial disease (PAD) or arterial injury detection.

ABI < 0.90 indicates significant PAD with 79-95% sensitivity and >95% specificity in patients.

Diabetic patients with neuropathy or ulcers show variable ABI accuracy for PAD detection, with sensitivity 29-100% and specificity 58-97%.

ABI helps in identifying and assessing risk for lower-extremity arterial injuries in trauma.

Potential arterial injury in stable patients following lower extremity blunt or penetrating trauma.

In diabetic patients the normal ABI results require cautious interpretation and potential further testing for guideline-directed medical therapy.

Indications

Diagnosis of peripheral arterial disease

Assessment of non-compressible arteries

Evaluation of vascular complication

Detection of arterial injury

Pre-surgical risk assessment

Contraindications

Acute limb ischemia

Severe pain/open wound

Non-Compressible Arteries

Recent surgery

Severe edema

Infection/cellulitis

Patients unable to stay supine during examination or those at risk of worsening extremity injuries with cuffs.

Avoid extremity compression in patients with DVT to prevent thrombus dislodging and embolization risks.

Outcomes

Low ABI suggests higher risk of heart attack, stroke, and cardiovascular mortality while high ABI indicates stiffness.

Associated with higher mortality and atherosclerosis marker. The ABI is a ratio of highest ankle to highest brachial systolic blood pressure.

ABI values reflect arterial disease progression or successful treatment outcomes.

Equipment required:

Blood Pressure Cuffs

Doppler Ultrasound Device

Doppler Gel

Measurement Tool

Sanitization Supplies

Patient Preparation:

Patient should wear loose clothing for easy arm and ankle access.

No anesthesia recommended as sedatives may affect blood pressure and ABI accuracy.

Position the patient supine, legs at heart level and ensure stillness for accurate measurements without movement interference.

Patient Positioning:

The patient must lie supine on an examination table, arms and legs level with the heart, resting for at least 10 minutes before measurement.

Standard Technique for ABI Measurement:

Choose a blood pressure cuff that is at least 40% of the limb’s circumference.

The ankle cuff should be positioned between the malleolus and calf, that allows space beneath for ultrasound gel to enable proper detection of brachial, dorsalis pedis, and posterior tibial pulses.

Measure brachial SBP in both arms, select the higher value, and palpate the pulse on the medial antecubital fossa.

Measure anterior and posterior tibial systolic pressures, then choose the higher value as the ankle pressure.

The DP pulse is felt on the dorsum between the first and second metatarsals, while the PT pulse is found near the medial malleolus.

Select the higher ankle SBP value, then divide it by brachial SBP to calculate the ABI.

Figure 1. ABI measurement for upper limb

Figure 2. ABI measurement for lower limb

Automated Technique for ABI Measurement:

Patient should rest adequately before procedure.

Attach four cuffs to limbs, then press “start” for the automated multicuff device to cycle. Results will appear on screen in 1 minute.

Complications:

Discomfort/pain

Skin Irritation/bruising

Aggravation of Pre-Existing Conditions

False results

Psychological distress

Inadequate/delayed diagnosis

References

Ankle Brachial Index – StatPearls – NCBI Bookshelf

References

Ankle Brachial Index – StatPearls – NCBI Bookshelf