The ankle-brachial pressure index (ABPI) is used to assess severity of peripheral arterial disease. An ABPI of 0.4 in a patient with rest pain and ulceration indicates which category of chronic limb-threatening ischaemia (CLTI)?

• A Fontaine stage III/IV (rest pain/tissue loss) — requires urgent revascularisation assessment ✓
• B Fontaine stage II (intermittent claudication) — no intervention needed
• C Non-compressible vessels giving falsely low ABPI — further evaluation with toe-brachial index needed
• D ABPI 0.4 is within normal range (0.4–1.2)

Explanation

Normal ABPI is 1.0–1.4. ABPI 0.7–0.9 indicates mild-to-moderate PAD with claudication; ABPI <0.5 indicates severe ischaemia. An ABPI of 0.4 with rest pain and ulceration represents Fontaine stage III/IV (CLTI — chronic limb-threatening ischaemia), which mandates urgent assessment for revascularisation (bypass or angioplasty/stenting) to prevent limb loss. Non-compressible vessels (diabetics, calcified arteries) give falsely ELEVATED (>1.3) ABPI, not falsely low. Normal ABPI range is 0.9–1.3, not 0.4–1.2.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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