Distinguishing features between VITT (vaccine-induced immune thrombotic thrombocytopenia), ITP (immune thrombocytopenia), and TTP (thrombotic thrombocytopenia)

	Syndrome
	VITT	ITP	TTP
Thrombocytopenia	Yes, typically 10,000 to 100,000/microL	Yes	Yes
Thrombosis	Yes, including atypical sites of venous and arterial thrombosis	Generally not seen, although there may be a slightly increased risk for VTE	Typically microvascular rather than VTE
Other clinical	Temporal relationship to specific COVID-19 vaccines Flu-like syndrome	Petechiae or purpura Often, otherwise well; often an incidental finding	Neurologic, kidney, and/or cardiac involvement may be seen
Other laboratory	Normal to slightly prolonged PT and aPTT Fibrinogen may be low D-dimer often markedly increased	Normal PT and aPTT Normal fibrinogen and D-dimer Normal hemoglobin (unless anemia from bleeding)	Normal PT and aPTT Normal fibrinogen and D-dimer Microangiopathic hemolytic anemia with laboratory findings of hemolysis and schistocytes on the blood smear
Diagnostic confirmation	Positive anti-PF4 antibody ELISA or functional assay	Diagnosis of exclusion	Severe ADAMTS13 deficiency (activity <10%)
Management implications*	Anticoagulation with a non-heparin agent Avoid heparin Avoid warfarin (unless platelet count has recovered) High-dose IVIG Minimize platelet and plasma transfusions	Platelet transfusions for critical bleeding Glucocorticoids or IVIG for serious bleeding or severe thrombocytopenia Rituximab, splenectomy, or TPO-RA in selected cases	Therapeutic plasma exchange Glucocorticoids Rituximab Caplacizumab in selected cases Avoid platelet transfusions unless major bleeding

Bolded text identifies some of the key distinguishing features of VITT. Hematologist input is advised to assist in distinguishing among these and other syndromes with thrombocytopenia and thrombosis.

VITT: vaccine-induced immune thrombotic thrombocytopenia; ITP: immune thrombocytopenia; TTP: thrombotic thrombocytopenia; VTE: venous thromboembolism; COVID-19: coronavirus disease 2019; PT: prothrombin time; aPTT: activated partial thromboplastin time; ELISA: enzyme-linked immunosorbent assay; IVIG: intravenous immune globulin; TPO-RA: thrombopoietin receptor agonist.
* This is only intended to summarize major differences in management and to emphasize the importance of making the correct diagnosis. Refer to UpToDate for detailed management discussions.

Graphic 131494 Version 1.0

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Distinguishing features between VITT (vaccine-induced immune thrombotic thrombocytopenia), ITP (immune thrombocytopenia), and TTP (thrombotic thrombocytopenia)