Immune paradoxes of vaccine-induced thrombotic thrombocytopenia (VITТ), heparin-induced thrombocytopenia (HIT) and thrombosis: from general mechanisms to the unique VITТ and HIT course

Aim : to carry out a comparative analysis of the pathogenesis, clinical manifestations, diagnostic criteria as well as therapeutic strategies of vaccine-induced thrombotic thrombocytopenia (VITТ) and heparin-induced thrombocytopenia (HIT), two rare but potentially life-threatening conditions associated with antibody-dependent platelet activation. Materials and Methods . Current data on the pathogenesis, epidemiology, clinical presentation, diagnosis, and treatment of VITТ and HIT have been reviewed including an analysis of existing diagnostic scoring systems, laboratory tests, and therapeutic approaches. The study is based on the data obtained from systematic reviews, clinical studies, and up-to-date clinical guidelines. Results . VITТ and HIT share a common pathophysiological mechanism involving the production of antibodies against platelet factor 4 (PF4) and subsequently developing thrombotic complications. However, a key difference lies in the triggers of the immune response: HIT is induced by heparin exposure, whereas VITТ develops following the administration of adenoviral vector vaccines against SARS-CoV-2. HIT is primarily characterized by venous thrombosis, while VITТ predominantly manifests with atypical thromboses, including cerebral venous sinus thrombosis. Both conditions require immediate medical intervention; however, HIT management involves discontinuation of heparin and the initiation of using alternative anticoagulants, whereas VITТ treatment requires administration of intravenous immunoglobulins and anticoagulants, including heparin-based agents. Conclusion . Despite their rarity, VITТ and HIT pose significant health risks to patients. Modern diagnostic methods, including the 4Тs scoring system and serological testing, facilitate the timely identification of HIT, whereas VITТ diagnostics remains a complex challenge and requires further standardization. Optimizing therapeutic strategies, including the use of novel anticoagulants and immunosuppressive approaches, is a priority task to reduce mortality and improve patient outcomes.