LAUSR

We recently reported on a 25-year-old female without a history of heparin exposure, presenting with thrombocytopenia, thrombosis, and elevated D-dimer levels 10 days after nine-valent human papillo-mavirus (HPV) vaccination ( Gardasil , Merck and Co). 1 The patient's samples activated platelet factor 4 (PF4)-treated platelets and recognized PF4 – polyanion complexes in heparin-induced thrombocytopenia (HIT) ELISA (PF4 – polyanion enzyme-linked immunosorbent assay). As previously noted, 1 thrombosis sites included the right internal iliac vein and bilateral pulmonary emboli. When it was that the patient had a vaccine-induced immune thrombotic thrombocytopenia (VITT)-like presentation, she was treated with intravenous immunoglobulin G (IVIg), to which she responded promptly. While these clini-cal and features are consistent with VITT, they overlap with spontaneous HIT, an IVIg-responsive condition where thrombosis and thrombocytopenia develop in the absence of proxi-mate heparin exposure.