ABSTRACT
Introduction.Vaccine induced immune thrombocytopenia and thrombosis (VITT) following ChAdOx1 nCOV-19 vaccine has been described, associated with unusual site thrombosis, thrombocytopenia, raised D-dimer and high titre immunoglobulin-G (IgG) class anti-Platelet Factor 4 (PF4) antibodies. Laboratory management of suspected cases begins with a sensitive anti PF4 antibodies binding assay (PF4-ELISA). If the PF4 binding assay is negative, this patient does not have Heparin induced Thrombocytopenia (HIT) or VITT. If the PF4 binding assay is positive, the positivity should be confirmed with one or multiple HIT functional assays as available, such as the serotonin release assay (SRA), heparin-induced platelet activation assay, platelet aggregation (PAT) test, flow cytometry test.Methods.We summarized clinical and laboratory findings of 7 patients in Piedmont who developed thrombosis and thrombocytopenia following AZD1222 vaccination. Plasma from all patients was used to test for anti PF4 antibodies by 2 different ELISA assays (Immucor and Stago) and by 2 different HIT functional assays, PAT and flow cytometry (HIT alert test) both performed in the presence of heparin, PF4 or both.Results.The 7 patients [6 males and 1 female, median age: 38 (range:31-76)] presented with thrombosis 2 to 17 days post vaccination: 5 males had deep vein thrombosis not in unusual sites, 1 male had stroke and the female had cerebral venous thrombosis (CVT). None had received heparin prior symptoms onset. Only 2 out of 7 patients tested positive for anti PF4 ELISA antibodies with both assays: the men with stroke showed low positivity (OD = 0,56 and 0,41) and the female with CVT strong positivity (OD = 3,2 and 3,87). Only the female patient with CVT tested positive with both HIT functional assays, PAT and HIT alert cytometry test in the presence of PF4 independently of heparin. Both assays were inhibited by high concentrations of heparin.Conclusions. In our limited experience VITT demonstrated to be an extremely rare event in the context of AZD1222 COVID-19 vaccination even in the subset of patients with thrombosis and thrombocytopenia.