Heparin-induced thrombocytopenia: Clinical considerations of alternative anticoagulation with various glycosaminoglycans and thrombin inhibitors

Heparin-induced thrombocytopenia (HIT), the most common complication of hep arin therapy, is also the most common form of the drug-induced thrombocytop enias. 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 characte rized by complexes of heparin and platelet factor (PF) 4. Enzyme-linked imm unosorbent assays allow easy and simple determination of these antibody tit ers; however, because specificity and sensitivity is not optimal, there is concern that the clinical relevance may be low. In clinical trials many pat ients were shown to form HIT-IgG in response to heparin without developing manifestations of HIT-type II. Therefore, routine screening of clinically a symptomatic patients for antiheparin/PF 4 antibodies is not recommended. HI T type TT is a clinicopathologic syndrome that ideally should be confirmed by laboratory testing. If any clinical suspicion arises, however, heparin a nd low molecular weight heparin therapy should be discontinued and an alter native anticoagulant therapy started. Alternative drugs have been evaluated in significant numbers of patients including danaparoid and thrombin inhib itors. 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 tes ting cannot be performed, immediate administration of a thrombin inhibitor is preferred.