Figure 1.

Platelet count abnormalities and clinical features. Normally, an increased platelet count increases the risk of thrombotic events, while a decreased platelet count increases the risk of bleeding. However, ET is a disease that presents with bleeding symptoms despite an increased platelet count. Diseases that present with thrombosis despite low platelet counts are termed TTS, which include HIT, VITT, PNH, APS, TMA, and DIC. TMA is classified as TTP, STEC-HUS, aHUS, secondary TMA, and other TMAs. Abbreviations: ET, essential thrombocythemia; ITP, idiopathic thrombocytopenic purpura/immune thrombocytopenia; TTS, thrombosis with thrombocytopenia syndrome; HIT, heparin-induced thrombocytopenia; VITT, vaccine-induced immune thrombotic thrombocytopenia; PNH, paroxysmal nocturnal hemoglobinuria; APS, antiphospholipid antibody syndrome; TMA, thrombotic microangiopathy; TTP, thrombotic thrombocytopenic purpura; STEC-HUS, Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome; aHUS, atypical hemolytic uremic syndrome; DIC, disseminated intravascular coagulation.