Table 1.

A clinical and immunological overview of HIT and VITT.

	HIT	VITT
Pathophysiology	Triggered by antibodies against PF4-heparin complexes [16]	Triggered by anti-PF4 specific antibodies, post vaccination [28]
Symptom onset	Typically 5–10 days after heparin administration [16]	Typically 4–42 days after adenovirus vector-based COVID-19 vaccine administration [28]
Clinical presentation	Thrombocytopenia, elevated risk of thrombosis [16]	Thrombocytopenia, high frequency of thrombosis at atypical sites like arterial and cerebral venous sinus [65]
Antibody characteristics and persistence	Transient anti-PF4/heparin antibodies, median duration of 50–80 days [73,74]	Persistent anti-PF4 antibodies, some cases exceeding 18 months [80,81]
Recurrence	Higher propensity for re-developing anti-PF4/heparin antibodies upon intra-operative heparin re-exposure. However, redevelopment of HIT is rare [74,76,77]	A subset of patients shows persistent thrombocytopenia and platelet-activating antibodies, with some cases of recurrent thrombosis and thrombocytopenia [80,82]
Recommended treatment	Non-heparin anticoagulant [42]	IVIG [17]