Some individuals with TTS may not have been evaluated for anti-PF4 antibodies; or have causes of thrombosis and thrombocytopenia other than VITT, such as antiphospholipid syndrome, cancer-associated thrombosis and thrombocytopenia, thrombotic thrombocytopenic purpura, or disseminated intravascular coagulation. Here, PF4 is linked to antiphospholipid syndrome.