Deterioration of vaccine‐induced immune thrombotic thrombocytopenia treated by heparin and platelet transfusion: Insight from functional cytometry and serotonin release assay

We report a case of a 62‐year‐old man who developed cerebral venous sinus thrombosis with subarachnoid hemorrhage and concomitant thrombocytopenia, which occurred 13 days after ChAdOx1 nCov‐19 injection. The patient died in the intensive care unit after heparin infusion and platelet transfusion. The key clinical purpose of this case report is to better understand how to confirm vaccine‐induced immune thrombotic thrombocytopenia (VITT). VITT diagnosis was made using (14)C‐serotonin release and flow cytometry evaluating activation and platelet microvesicles on washed platelets. Four control patients were examined: a patient with heparin‐induced thrombocytopenia (HIT), two patients with thrombotic events without thrombocytopenia after ChAdOx1 nCov‐19 or BNT162b2, and a patient with suspected HIT and an excluded diagnosis. We evidenced in the VITT case a high level of IgG anti–platelet factor 4–heparin antibodies associated with a high level of platelet activation in the absence of heparin. Conversely, the functional assays were negative in the patients with thrombosis without thrombocytopenia.