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AT Deficiency Perioperative — RACP Adult Medicine MCQ

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HardHaematologyAT Deficiency PerioperativeRACP Adult Medicine

A 45-year-old man with a history of recurrent deep venous thrombosis is found to have antithrombin deficiency (AT level 45%, normal 80–120%). He is on warfarin. He requires urgent surgery. What is the critical perioperative consideration?

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Correct answer: A — No bridging needed – warfarin can be continued

Antithrombin (AT) is the essential cofactor for heparin's anticoagulant activity. In patients with AT deficiency, heparin is LESS EFFECTIVE because there is insufficient AT for heparin to activate. During the perioperative period when heparin bridging is needed, AT concentrate replacement (to achieve AT levels >80%) may be required to ensure adequate heparin effect. Without AT supplementation, patients may have 'heparin resistance' – requiring very high doses with subtherapeutic aPTT/anti-Xa levels. AT concentrate is available in Australia (Antithrombin III concentrate). DOACs do NOT require AT for their mechanism and may be an alternative in non-surgical situations.

Reference: eTG – 2025 – Haematology; National Blood Authority – 2024