Relationships between PF4-dependent IgG binding to platelets and p-selectin expression, serotonin release in SRA, and OD in PF4 ELISA observed in studying 57 identity-blinded HIT samples. (A-C) Ordinate depicts fold increase in PF4-dependent p-selectin expression relative to value obtained with normal control serum, percentage serotonin release, and PF4 ELISA OD, respectively. In addition, abscissa depicts fold increase in PF4-dependent IgG binding relative to value obtained with normal serum. SRA-positive and SRA-negative HIT sera are depicted by filled and open circles, respectively.