Representative reactions of patient Abs. Patient samples were tested against platelets pretreated with eptifibatide (E), tirofiban (T), xemilofiban (X), orbofiban (O), and RGDW peptide (R). (A) Serum from a typical patient with eptifibatide-induced thrombocytopenia reacted with platelets pretreated with eptifibatide (solid tracing) but not with untreated platelets (dashed tracing) using flow cytometry. (B) The same serum failed to recognize platelets pretreated with T, X, O, and R. (C) A second patient sample reacted with platelets pretreated with E or R. (D) A third Ab recognized platelets pretreated with each of the 5 ligands. Reactions of patient serum with untreated platelets and normal serum with treated platelets were negative (not shown). Horizontal dashed line indicates upper limit of normal (mean + 3.0 SD). (B-D) Values on the ordinate indicate ratio of median fluorescence intensity value obtained with ligand-treated platelets to value obtained with untreated platelets.