Heparin-induced Thrombocytopenia: Clinical Considerations of Alternative Anticoagulation with Various Glycosaminoglycans and Thrombin Inhibitors

Abstract

Heparin-induced thrombocytopenia (HIT), the most common complication of heparin therapy, is also the most common form of the drug-induced thrombocytopenias. HIT is classified as type I and type II, the first being benign and the latter severe. HIT type II is attributed to an immune response characterized by complexes of heparin and platelet factor (PF) 4. Enzyme-linked immunosorbent assays allow easy and simple determination of these antibody titers; however, because speci ficity and sensitivity is not optimal, there is concern that the clinical relevance may be low. In clinical trials many patients were shown to form HIT-IgG in response to heparin without developing manifestations of HIT type II. Therefore, routine screening of clinically asymptomatic patients for antiheparin/ PF 4 antibodies is not recommended. HIT type II is a clinico pathologic syndrome that ideally should be confirmed by labo ratory testing. If any clinical suspicion arises, however, heparin and low molecular weight heparin therapy should be discon tinued and an alternative anticoagulant therapy started. Alter native drugs have been evaluated in significant numbers of patients including danaparoid and thrombin inhibitors. In the case of danaparoid, it is highly recommended that an in vitro test for cross-reactivity be performed before the onset of therapy. If testing cannot be performed, immediate administra tion of a thrombin inhibitor is preferred. Key Words: Plate lets—Heparin—Thrombocytopenia—Anticoagulants.