Platelet activation markers, with and without in vitro stimulation, stratified by bleeding score in ITP patients. (A-B) Percentages of unstimulated (No Agonist), ADP-, and TRAP-stimulated activated GPIIb-IIIa–positive and P-selectin–positive platelets, respectively, in ITP patient blood, stratified by bleeding score (bleeding score 0, n = 18; 1, n = 22; 2, n = 11; and 3 or 4, n = 6). (C-E) Platelet surface density (as measured by geometric MFI) of activated GPIIb-IIIa (C), P-selectin (D), and GPIb (E) on unstimulated and in vitro-stimulated platelets. Results shown are means ± SEM. P values (above each data set) are for univariate ordinal logistic regressions with respect to bleeding score.