Table 3.

Diseases that should be differentiated from VITT and their key considerations.

Disease Name	Abbreviation	Important Clinical and Laboratory Findings
Heparin-induced thrombocytopenia	HIT	History of exposure to heparin, 4T’s score
Thrombotic microangiopathy	TMA	Appearance of schizocytes (peripheral blood smear), marked decrease in haptoglobin
Thrombotic thrombocytopenic purpura	TTP	A type of TMA with markedly reduced ADAMTS13 activity with ADAMTS13 inhibitor
Immune thrombocytopenia	ITP	Diagnosis of exclusion. Increased megakaryocytes in bone marrow and positive antiplatelet antibodies assist in diagnosis
Antiphospholipid antibody syndrome	APS	Positive for at least one of the following antibodies: lupus anticoagulant; anticardiolipin antibody; and anti-β2 GPI antibody
Paroxysmal nocturnal hemoglobinuria	PNH	Hemolysis (normocytic anemia, elevated reticulocyte, elevated indirect bilirubin, elevated LDH, decreased haptoglobin), presence of PNH type-cells (CD55/59-negative)
Disseminated intravascular coagulation	DIC	PT, APTT, fibrinogen, FDP, D-dimer, AT, TAT, PIC, plasminogen, α2PI

Abbreviations: VITT, vaccine-induced immune thrombotic thrombocytopenia; TMA, thrombotic microangiopathy; ADAMTS13, a disintegrin-like and metalloproteinase with thrombospondin type 1 motifs 13; GP, glycoprotein; LDH, lactate dehydrogenase; PT, prothrombin time; APTT, activated partial thromboplastin time; FDP, fibrin/fibrinogen degradation products; AT, antithrombin; TAT, thrombin-antithrombin complex; PIC, plasmin-αplasmin₂ inhibitor complex; α₂PI, α₂ plasmin inhibitor.