Purpose: To review recent developments in the pathogenesis, clinical features, laboratory testing and treatment of heparin-induced thrombocytopenia (HIT).
Methods: Narrative review of the literature, including relevant papers published in English or French.
Principal findings: Although the prevalence of HIT has decreased with the widespread use of low molecular weight heparin in the past ten years, HIT remains a life-threatening prothrombotic state. This immune adverse event due to heparin-dependent antibodies that bind to chemokines (such as platelet factor 4) induces platelet activation and hypercoagulability. Heparin-induced thrombocytopenia can be complicated by thrombosis even after withdrawing heparin, explaining why substituting heparin with an alternative anticoagulant (danaparoid, lepirudin, argatroban) is always necessary. However, management of these alternative treatments is difficult, and in some patients there is the risk of withdrawing heparin without taking the time to diagnose HIT properly on the basis of clinical and laboratory findings (evolution of platelet count, laboratory testing such as antigen assays and platelet activation tests).
Conclusions: Management of HIT has become easier in recent years with the development of more specific and sensitive laboratory tests and new antithrombotic drugs. However, the diagnosis of HIT is often difficult, and it remains very important to investigate this adverse reaction systematically in every patient treated with heparin who develops thrombocytopenia.