Approach to evaluating and treating suspected VITT (vaccine-induced immune thrombotic thrombocytopenia)

VITT is an exceedingly rare condition (likely <1 in 100,000) that has been linked to certain vaccinations for COVID-19. The risk of life-threatening thrombosis from COVID-19 exceeds the risk of VITT from vaccination by over 100-fold. Venous and arterial thromboses have occurred, with typical sites of VTE as well as atypical sites (cerebral venous sinus thrombosis [CVST], splanchnic venous thrombosis). Diagnosis is made by demonstrating anti-PF4 antibodies by ELISA or functional assay in an individual with the appropriate clinical history. Rapid immunoassays for HIT (latex-enhanced; chemiluminescence) cannot be used to exclude VITT because these assays are usually negative for VITT antibodies. The main treatment is anticoagulation with anticoagulation and IVIG. A non-heparin anticoagulant should be used if there is any diagnostic uncertainty between VITT and HIT (including autoimmune or delayed HIT). Prophylactic aspirin is not recommended after vaccination, as it increases bleeding risk without any evidence it reduces the risk of VITT.

VITT: vaccine-induced thrombotic thrombocytopenia; COVID-19: coronavirus disease 2019; IVIG: intravenous immune globulin; DVT: deep vein thrombosis; CVT: cerebral venous thrombosis; CBC: complete blood count; ELISA: enzyme-linked immunosorbent assay; PT: prothrombin time; aPTT: activated partial thromboplastin time; ITP: immune thrombocytopenia; DOAC: direct oral anticoagulant; LMW: low molecular weight.
* In addition to the AstraZeneca and Janssen/Johnson and Johnson vaccines, other adenoviral vectored COVID-19 vaccines include Sputnik V and CanSino. VITT has not been reported with Sputnik V or CanSino, but clinical trial data are more limited with these vaccines.
¶ Coagulation tests (PT, aPTT, fibrinogen, D-dimer) may be obtained on presentation or later (after results of other testing are reviewed). A very high D-dimer and low fibrinogen are supportive of VITT and may be especially helpful in distinguishing VITT from ITP in individuals without thrombosis. PT and aPTT are obtained before anticoagulation is initiated.
Δ Platelet counts that show thrombocytopenia prior to vaccination argue against the diagnosis of VITT. In some cases, an individual with VITT might have only mild thrombocytopenia if early in the disease course or if their baseline platelet count is higher than average (eg, a decrease from a baseline platelet count of 400,000/microL to 150,000/microL might be significant and argue for VITT).
◊ Concerning features that may warrant plasma exchange include severe thrombocytopenia (platelet count <30,000/microL) plus CVT or severe thrombocytopenia plus extensive thrombosis.

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Approach to evaluating and treating suspected VITT (vaccine-induced immune thrombotic thrombocytopenia)