Platelet responsiveness to collagen and GPVI stimulation is reduced in severely injured patients. (A) Platelets from healthy volunteers (n = 10) or trauma patients (n = 14) were labeled with mepacrine (10 μM, green) in whole blood and perfused over collagen at arterial shear rates (1000/s). (i) Representative images after a 5-minute perfusion. Bars represent 25 μm. (ii) Area coverage over time in trauma patients and healthy volunteers. (iii) Area coverage at 5 minutes. (B-D) Platelet aggregometry in PRP from healthy volunteers (blue; n = 10) and trauma patients (red; n = 20) after a 5-minute stimulation with collagen (B), CRP-XL (C) or ADP (D) at 1200 rpm. (E) Platelet P-selectin expression (% positive) measured by flow cytometry after stimulation with CRP-XL (0.1 μg/mL) or ADP (10 μM) for 5 minutes. Two-way ANOVA with Šidák’s multiple-comparisons test (Aii,B-D) or Student t test (Aiii). *P < .05; **P < .01; ***P < .001. n.s., not significant.