Endothelial thromboinflammation develops in the Endo-chip in response to both VITT ELISA positive and negative sera. (A) Optical density (OD) of VITT samples that tested positive by routine PF4/polyanion ELISA (VITT ELISA positive), and negative by routine PF4/polyanion ELISA (VITT ELISA negative). The OD was also measured for samples from patients with VTE without VITT and in vax controls. The dotted black lines represent the lowest and highest cutoff for positivity determined by the manufacturer. (B) Platelet (green), neutrophil (red), and fibrin (purple) accumulation following a 15-minute blood perfusion in the Endo-chip after treatment with VITT ELISA positive, VITT ELISA negative, VTE without VITT, or vax control sera. Representative images. (C) Platelet fluorescence area per field, neutrophil count per field, and fibrin fluorescence area per field following a 15-minute perfusion of blood in the Endo-chip after treatment with VITT ELISA positive, VITT ELISA negative, VTE without VITT, or vax control sera. VITT ELISA positive n = 15, VITT ELISA negative n = 17, VTE no VITT n = 8, and vax control n = 15. The individual patient numbers are shown in panel A. One-way ANOVA with Dunn post hoc test was used for comparisons.