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Ankle–Brachial Pressure Index (ABPI)



Ankle–Brachial Pressure Index (ABPI)

Definition

Ankle–Brachial Pressure Index (ABPI), also called Ankle–Brachial Index (ABI), is a simple, non-invasive bedside test that compares systolic blood pressure at the ankle with systolic blood pressure at the brachial artery to assess lower-limb arterial perfusion.

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Principle


Peripheral arterial disease (PAD) causes reduced systolic pressure distal to arterial stenosis or occlusion. Comparing ankle pressure with arm pressure provides an objective estimate of arterial flow to the legs.



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Formula


ABPI =

Highest ankle systolic pressure (dorsalis pedis or posterior tibial) ÷ Highest brachial systolic pressure


Measured separately for each leg.



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Methods of Measuring ABPI


1. Doppler-Assisted ABPI (Gold Standard)


Equipment


Hand-held Doppler (8–10 MHz)


Sphygmomanometer cuffs (appropriate size)



Steps


1. Patient rests supine for ≥10 minutes



2. Measure systolic BP in both brachial arteries using Doppler



3. Measure systolic BP at:


Dorsalis pedis artery


Posterior tibial artery




4. Use the higher ankle pressure and higher brachial pressure for calculation




Advantages


Most accurate bedside method


Widely recommended in guidelines



Limitations


Requires operator skill


Time-consuming in busy clinics




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2. Automated Oscillometric ABPI


Description


Automated BP devices measure arm and ankle pressures simultaneously or sequentially



Advantages


Quick


Minimal training required



Limitations


Less accurate in:


Diabetes


Chronic kidney disease


Severe PAD



May underestimate disease severity




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3. Toe–Brachial Index (TBI) (When ABPI is Unreliable)


Indications


Non-compressible arteries (ABPI >1.3)


Diabetes mellitus


Medial arterial calcification



Normal TBI


≥0.7




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Interpretation of ABPI


ABPI Value Interpretation


1.00 – 1.30 Normal

0.91 – 0.99 Borderline

0.41 – 0.90 Mild–Moderate PAD

≤0.40 Severe PAD

>1.30 Non-compressible arteries




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Clinical Uses of ABPI


1. Diagnosis of Peripheral Arterial Disease


Detects symptomatic and asymptomatic PAD


Correlates with angiographic disease severity



2. Cardiovascular Risk Stratification


Low ABPI is an independent predictor of:


Myocardial infarction


Stroke


Cardiovascular mortality




3. Assessment of Leg Pain


Differentiates vascular claudication from:


Neurogenic claudication


Musculoskeletal pain




4. Wound and Ulcer Assessment


Guides safety of compression therapy in venous ulcers


Predicts wound healing potential



5. Pre- and Post-Revascularization Evaluation


Baseline assessment before intervention


Objective follow-up after angioplasty or surgery




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Contraindications / Cautions


Severe leg pain or acute limb ischemia (do not delay urgent care)


Incorrect cuff size can produce false results


Calcified arteries may falsely elevate ABPI




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Factors Affecting Accuracy


Diabetes mellitus


Chronic kidney disease


Advanced age


Edema


Improper patient positioning




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Key Points


ABPI is a rapid, inexpensive, and non-invasive test


Doppler-assisted method is preferred for accuracy


Abnormal ABPI indicates both limb ischemia and systemic atherosclerosis


High values (>1.3) are not normal and require alternative assessment




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