CardiologyTier 2Topic

Ankle-brachial index and arterial Dopplers

Principle

ABI = ratio of ankle systolic BP to brachial systolic BP - a simple, non-invasive screening test for peripheral arterial disease
First-line test in suspected PAD, performed before more advanced vascular imaging

Interpretation

ABI	Interpretation
>1.3	Non-compressible vessels (calcification) - falsely elevated, common in diabetes/CKD - use toe-brachial index instead
0.9-1.3	Normal
0.7-0.9	Mild PAD
0.4-0.7	Moderate PAD (often claudication)
<0.4	Severe PAD (critical limb ischaemia risk)

Doppler waveforms and exercise ABI

Continuous-wave Doppler assesses waveform (triphasic normal -> biphasic -> monophasic with worsening disease) alongside pressure measurement
Exercise ABI unmasks PAD when resting ABI is normal but symptoms suggest claudication

Acting on the result

Guides referral urgency and compression therapy safety - compression bandaging is contraindicated if ABI <0.8 in leg ulcer management, a key patient-safety cross-link

Associations

Peripheral arterial disease, diabetic vascular calcification, leg ulcer management

Serial testing

Serial ABI can track disease progression, though symptom-based reassessment matters more than the absolute number for management decisions

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