Distribution of platelet count, d-dimer level, and ELISA optical density (OD) for patients with VITT compared with patients without VITT, with or without thrombosis. As shown in (A), there is a significant difference in the median platelet count between the 3 groups. Similarly, median d-dimer levels (B) and median ELISA OD values (C) showed significant differences across the 3 groups. As shown in the figure, 23 patients in the non-VITT group had thrombotic events. Of these 23 patients, 3 had d-dimer levels ≥2.0 mg/L FEU and platelets <150 000/mm³. These 3 patients had negative PF4-ELISA and SRA results. Ten of the 23 patients with thrombosis had d-dimer ≥2.0 mg/L FEU, but their platelet counts were normal. These patients also had negative PF4-ELISA and SRA results. The other 10 patients in the non-VITT with thrombosis group had d-dimer <2.0 mg/L FEU and had normal platelet counts. These patients had negative PF4-ELISA results, but SRA was not performed due to a low likelihood for VITT (according to the National Institute for Health and Care Excellence guideline).⁶  In (C), 1 patient had a positive PF4-ELISA (OD, 1.98) confirmed by positive SRA (see Table 1).