[Management of HIT/anti-PF4 disorders]

Heparin-induced thrombocytopenia (HIT) was widely known as a disease characterized by development of thrombosis with thrombocytopenia after heparin exposure. In addition, vaccine-induced immune thrombotic thrombocytopenia (VITT) has been described as a fatal disease involving simultaneous bleeding and thrombosis after COVID-19 adenovirus vector vaccination. These were caused by HIT antibodies and anti-PF4 antibodies, respectively, but both were autoantibodies that recognized PF4, and were found to have the same pathology with different severities. In recent years, many pathologies in which anti-PF4 antibodies are produced have been reported, and a new concept of anti-PF4 disorder has been proposed. Anti-PF4 disorders are often difficult to identify due to their diverse range of causes, and the prognosis varies greatly depending on whether anti-PF4 antibodies can be measured and early treatment performed after observation of thrombocytopenia of unknown cause or thrombosis at an unusual site. To avoid overlooking anti-PF4 disorders, clinicians should become familiar with the classification of these disorders and accurately select the necessary tests.