Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a highly prothrombotic disorder caused by anti-PF4 antibodies that activate platelets and neutrophils, leading to thrombosis. Heparin-induced thrombocytopenia (HIT) is a related anti-PF4 mediated disorder, with similar pathophysiology and clinical manifestations but different triggers (i.e., heparin vs adenoviral vector vaccine). Clinically, both HIT and VITT typically present with thrombocytopenia and thrombosis, although the risk of thrombosis is significantly higher in VITT, and the thromboses occur in unusual anatomical sites (e.g., cerebral venous sinus thrombosis and hepatic vein thrombosis). The diagnostic accuracy of available laboratory testing differs between HIT and VITT; for VITT, ELISAs have better specificity compared to HIT and platelet activation assays require the addition of PF4. Treatment of VITT and HIT is anticoagulation non-heparin anticoagulants; however, heparin may be considered for VITT if no other option is available.

A 56-year-old male presented to the emergency department with a four-day history of suprapubic pain and hematuria. The patient started ciprofloxacin 3 days prior to treat a suspected urinary tract infection (UTI) but his symptoms had not improved. History revealed that the patient had had recurrent UTIs for approximately 2 years in the setting of spinal cord injury following a car-pedestrian accident at age of 3 years. A complete blood count (CBC) revealed a low platelet count of 27 Â 10 9 /L (reference range, 150-400); the white blood cell (WBC) count was 10.1 Â 10 9 /L (reference range, 4.0-11.0), with normal absolute neutrophil count of 6.3 Â 10 9 /L (reference range, 2.0-7.5). The hemoglobin was 12.0 mg/dL (reference range, 13.0-18.0). Low platelet count in the context of potential UTI can indicate alife-threatening problem such as septicemia with or without associated disseminated intravascular coagulation (DIC) 1 or a serious underlying marrow disorder, such as acute leukemia. DIC can be complicated by hemorrhage, thrombosis, or both, but in this case, it is