Clinical examination and the ankle–brachial pressure index usually establish the presence and severity of limb ischaemia. Imaging defines arterial involvement, while blood tests identify treatable secondary causes.
Ankle–brachial pressure index
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The ankle–brachial pressure index is the ratio of the highest systolic ankle blood pressure to the highest systolic brachial blood pressure.
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The index is over 1.0 in health, typically 0.5–0.9 in intermittent claudication, and usually below 0.5 in critical limb ischaemia.
Imaging
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Duplex ultrasonography, MRI or CT with intravenous contrast agents may further characterise the sites of arterial involvement.
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Intra-arterial digital subtraction angiography is used in patients undergoing endovascular revascularisation.
Tests for treatable secondary causes
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A full blood count looks for thrombocythaemia, lipid testing looks for hyperlipidaemia, and blood glucose testing looks for diabetes mellitus.