Synopsis
Perform and interpret ABPI with arterial waveforms, recognise unreliable measurements, and choose appropriate confirmatory physiological or anatomical tests.
- Rest the patient supine and measure both arms and both ankle arteries.
- For each leg, divide the highest ankle pressure by the highest arm pressure.
- Record Doppler signal character and technical limitations alongside the numeric index.
Key red flags
New paralysis or paraesthesia in a painful cold limb requires emergency vascular discussion.
Tissue loss or rest pain with a normal or high ABPI may still represent severe ischaemia.
An unobtainable ankle signal in a symptomatic limb requires prompt clinical escalation rather than repeated cuff inflation.
Rest pain, ulceration, gangrene or marked waveform abnormality remains concerning even when the calculated ankle index appears normal or raised.
Sudden pain, pallor, coldness, pulse loss, paraesthesia or paralysis requires emergency assessment and should not wait for a complete outpatient protocol.
Investigation priorities
Quantify resting ankle-to-arm systolic pressure for each lower limb.
Management branches
A person with diabetes has exertional calf pain and a technically high ankle pressure.
- Inputs: right arm 142 mmHg, left arm 136 mmHg, right dorsalis pedis 168 mmHg and right posterior tibial 174 mmHg, with a damped monophasic pedal signal.
- Calculation and reasoning: 174 divided by 142 gives 1.23, but diabetes, unexpectedly high ankle pressure and a damped monophasic waveform make incompressibility and occult PAD plausible.
Stable symptoms or examination findings justify resting physiological assessment for PAD.