Reviews
Vol. 3 No. 2 (2024)
Recent advances in classic heparin-induced thrombocytopenia (HIT), autoimmune HIT, spontaneous HIT, and vaccine-induced immune thrombotic thrombocytopenia
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All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
Received: 2 March 2024
Accepted: 9 June 2024
Accepted: 9 June 2024
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Anti-platelet factor 4 (PF4) disorders are a group of platelet-consumptive disorders characterized by platelet-activating antibodies against PF4, thrombocytopenia and an increased risk of thrombosis. PF4 is a chemokine released by platelet alpha granules upon activation, which can form immune complexes with negatively charged substances, such as heparin, cartilage components, nucleic acids, and viral and bacterial agents. Antibodies formed in response to PF4-polyanion complexes may display platelet-activating properties and cause pan-cellular activation, leading to the marked prothrombotic state of anti-PF4 disorders. In recent years, the landscape of anti-PF4 disorders has evolved to include classic heparin-induced thrombocytopenia (cHIT), autoimmune HIT (aHIT), spontaneous HIT (SpHIT), vaccine-induced immune thrombotic thrombocytopenia (VITT), and the newly recognized spontaneous VITT (SpVITT). These disorders have garnered increased attention due to their association with severe clinical outcomes. Recent discoveries have expanded the understanding of these conditions, highlighting the role of various triggers, such as upper respiratory tract infections and monoclonal gammopathy of undetermined significance, in their development. Compared to cHIT, the less common anti-PF4 disorders VITT, aHIT, SpHIT and SpVITT generally appear more severe, with aggressive disease courses, more severe thrombocytopenia and a higher frequency of bleeding, thrombosis at unusual sites, involvement of the central nervous system and of multiple vascular beds. Clinical suspicion and knowledge of the less well-known triggers of anti-PF4 disorders are pivotal to ordering the appropriate laboratory tests and initiating the necessary treatments. Herein, we will review cHIT, aHIT, SpHIT and VITT, focusing on their clinical presentation and therapeutic management.
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1.
Clerici B, Scavone M, Podda GM. Recent advances in classic heparin-induced thrombocytopenia (HIT), autoimmune HIT, spontaneous HIT, and vaccine-induced immune thrombotic thrombocytopenia. Bleeding Thromb Vascul Biol [Internet]. 2024 Jun. 20 [cited 2025 Nov. 8];3(2). Available from: https://www.btvb.org/btvb/article/view/127
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