Mechanisms of Thrombosis in Heparin-Induced Thrombocytopenia and Vaccine-Induced Immune Thrombotic Thrombocytopenia

Abstract

Heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT) are rare, iatrogenic immune-mediated conditions with high rates of thrombosis-related morbidity and mortality. HIT is a long-recognized reaction to the administration of the common parenterally administered anticoagulant heparin (or its derivatives), while VITT is a new, distinct syndrome occurring in response to adenovirus-based vaccines against coronavirus disease 2019 and potentially other types of vaccines. A feature of both HIT and VITT is paradoxical thrombosis despite a characteristic low platelet count, mediated by the presence of platelet-activating antibodies to platelet factor 4. Several additional factors have also been suggested to contribute to clot formation in HIT and/or VITT, including monocytes, tissue factor, microparticles, endothelium, the formation of neutrophil extracellular traps, complement, procoagulant platelets, and vaccine components. In this review, we discuss the literature to date regarding mechanisms contributing to thrombosis in both HIT and VITT and explore the pathophysiological similarities and differences between the two conditions.

2024 Eberhard F. Mammen Award Announcements: Part I—Most Popular Articles

“…Consequently, the most popular papers from each category are identified separately. Tables 3 and 4 respectively list the top 25 downloaded articles from STH in 2023 (from 2022 and 2023 inclusive), as eligible for either the “free access” ( Table 3 ) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 or “general category” ( Table 4 ) 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 awards.…”

“…As 2023 is no longer considered a pandemic, and as journals transition back to “business as usual,” COVID-19 papers, while remaining popular, do not seem to entirely dominate as in the recent past. Nevertheless, 16/25 papers in the top 25 list have some connection to COVID-19, with 4 of these actually related to vaccine-induced immune thrombotic thrombocytopenia (VITT), 2 7 12 15 a rare but serious condition arising from vaccination against COVID-19.…”

Editorial Compilation—XIII

“…This issue of STH continues with a second Young Investigator winner, Dr. Maria Selvadurai, this time part of the 2020 award “team.” 4 Dr. Selvadurai and coauthors provide a state-of-the-art review on the mechanisms of thrombosis in heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT). 5 Both HIT and VITT are rare, iatrogenic immune-mediated conditions with high rates of thrombosis-related morbidity and mortality. HIT is a long-recognized reaction to the administration of the common parenterally administered anticoagulant heparin (or its derivatives), 6 7 while VITT is a new, distinct syndrome occurring in response to adenovirus-based vaccines against coronavirus disease 2019 (COVID-19) and potentially other types of vaccines.…”

Evolution of Hemostasis Testing: A Personal Reflection Covering over 40 Years of History*

“…Whereas HIT can occur in some 1 to 3% of exposures to unfractionated heparin, VITT only occurs in around 1/50,000 to 1/100,000 doses of vaccine, with only adenovirus-based vaccines consistently confirmed as being associated with VITT. 122 123 Although relatively rare, VITT became a major preoccupation of many of us active in the hemostasis field, especially given its connection to COVID-19 vaccine use and thrombosis associated with thrombocytopenia. As part of the THANZ (Thrombosis and Haemostasis Society of Australia and New Zealand) group charged to diagnose and manage the unfolding VITT crisis in Australia, we held regular out of normal work hours Thursday evening meetings for almost a year devising diagnostic and management strategies and discussing our cases.…”