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Coagulation

Therapy related coagulopathies

Heparin

Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 12 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

General
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● Also called unfractionated heparin
● Short acting anticoagulant with half life of approximately 90 minutes

Mechanism of action
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● Derived from porcine intestinal mucosa or bovine lung, which contain heparin-rich mast cells
● Markedly enhances activity of antithrombin, which inhibits activated factors II, IX, X, XI, XII, kallikrein and probably VII, but doesn’t cause a true decrease in factor levels
● Most heparin preparations are heterogeneous, with a molecular weight between 7-25K daltons
● Anticoagulant activity is variable, since only 1/3 of heparin molecules have the pentasaccharide sequence necessary for antithrombin mediated anticoagulant activity

Clinical features
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● Used as initial anticoagulant therapy, to treat deep venous thrombosis, post-operatively and for other short-term indications
● Decreases morbidity and mortality from acute thrombotic disease
● Complications include hemorrhage (overcoagulation) and heparin-induced thrombocytopenia (up to 3% of patients)
● Recommended that 90% of patients should achieve therapeutic anticoagulation within 24 hours

Monitoring
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● Recommended to monitor with PTT assay (that has been standardized using determination of heparin levels), activated clotting time (if high heparin levels present, as during cardiopulmonary bypass surgery, since no clotting occurs at these levels with PTT) or heparin levels assayed by measuring activity against factor Xa (therapeutic range is 0.3 to 0.7 anti-Xa units/ml) within 12 hours (Clin Lab Med 2009;29:283)
● Also monitor platelet count within 72 hours, with platelet monitoring to continue periodically for 20 days; PT is usually normal
● Note: often the cause of prolonged PTT is heparin in sample collected through indwelling line; identify by treating with heparinase

Diagrams
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Heparin 2-D structure


Function of heparin

Treatment
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● Protamine sulfate (for emergency reversal of heparin)

End of Coagulation > Therapy related coagulopathies > Heparin

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