Diagnostic potential of PP flow cytometry assay in identifying VITT plasma. (A) Receiver-operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic potential of fold-increase compared with no plasma baseline in PP formation in healthy donors induced by plasma from patients with confirmed VITT (n = 23) who tested positive on both ELISA and SRA, and VITT-negative patients (n = 24) who tested negative on both ELISA and SRA, and ELISA false-positive patients who are non-thrombocytopenic and SRA-negative. (B) ROC analysis of the fold-change in PP proportion in the presence of the FcγRIIa-blocking antibody IV.3 (10 µg/mL) relative to SFLLRN alone. Supplemental Tables 1 and 2 provide lists of sensitivity and specificity at various cutoff values. Representative patterns of PP response demonstrating classical VITT (C), heparin-enhancing VITT (D), and negative profile (E). PP response of individual patients in the development cohort are shown in panels F, G, and H. Dotted horizontal line represents no plasma baseline. AUC, area under the curve.