LAUSR

Vaccine-induced immune thrombotic thrombocytopenia (VITT) has emerged as a rare side effect of adenoviral vector-based vaccines against Coronavirus disease 2019 (COVID-19), and it is most frequently reported after Vaxzevria (AstraZeneca) vaccine. We described a case of severe thrombocytopenia associated with massive pulmonary embolism and portal vein thrombosis, occurring 13 days after the administration of the single dose adeno viral vector-based vaccine Ad26.COV2.S (Janssen vaccines, Leiden, Netherlands). Based on an early clinical suspect, the patient quickly received treatment with corticosteroids and intravenous immunoglobulins, followed by a rapid increase in platelet count that allowed full dose anticoagulation to be timely administered. Treatment with intravenous immunoglobulins, however, could mask the ability of anti-PF4-heparin antibodies to bind and activate platelets in the presence of heparin, leading to false negative results at the immunoassay functional test. Therefore, if VITT is suspected, blood samples for diagnostic confirmation should be collected prior to any treatment to improve diagnostic performance.