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521) A 79-year-old man with diabetes, hypertension, and hyperlipidemia underwent a single vessel coronary artery bypass graft 4 years ago. His hospitalization was complicated by heparin-induced thrombocytopenia (HIT) without thrombotic complications, and his platelet count returned to normal after discontinuation of heparin. He is now admitted for a reoperation to perform a three-vessel coronary artery bypass. The anti-heparin/platelet factor-4 IgG enzyme-linked immunoabsorbent assay (ELISA) result is negative and the serotonin release assay result is negative. What is the most appropriate intraoperative management for anticoagulation of the bypass circuit?

Anticoagulation with unfractionated heparin. Anticoagulation with bivalirudin. Anticoagulation with argatroban. Cancel surgery indefinitely. Delay surgery until anti-heparin/platelet factor-4 IgG, IgA, and IgM ELISA is performed.

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• Heparin induced thrombocytopenia (HIT) is an immune complication of heparin therapy that can lead to life-threatening arterial and venous thrombosis.

• HIT is characterized by a drop in the platelet count by approximately 50% within 5 to 10 days of the initiation of heparin therapy and can be associated with the development of thrombosis.

• The anti-heparin/platelet factor-4 (PF4) enzyme-linked immunoabsorbent assay (ELISA) result is often used to screen for the antibodies implicated in causing HIT. Although this assay is highly sensitive, it has poor specificity. The serotonin release assay is a functional assay that assesses the presence of anti-heparin/PF4 antibodies that can activate platelets. This assay has high sensitivity and specificity (98% and 95%, respectively).

• If a patient has a remote history of HIT with negative immunologic and functional assay results for HIT, unfractionated heparin can be used for cardiovascular surgery.

• If a patient has acute HIT with positive immunologic and functional assays for HIT, unfractionated heparin should not be used for cardiovascular surgery. Surgery can be delayed until the assay results are negative and then unfractionated heparin can be used. If surgery cannot be delayed, then an agent such as bivalirudin can be used as an alternate anticoagulant.

Linkins LA, Dans AL, Moores LK, et al: Treatment and prevention of heparin-induced thrombocytopenia:antithrombotic therapy and prevention of thrombosis, 9th ed. American College of Chest Physicians Evidence-based clinical practice guidelines. Chest 2012;141(suppl):e495S–e530S.

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Clinical Pathology: Hematology & Coagulation, Transfusion Medicine

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